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Dorsal stream involvement in recognition of objects with transient onset but not with ramped onset

Dorsal stream involvement in recognition of objects with transient onset but not with ramped onset Background: Although the ventral visual stream is understood to be responsible for object recognition, it has been proposed that the dorsal stream may contribute to object recognition by rapidly activating parietal attention mechanisms, prior to ventral stream object processing. Methods: To investigate the relative contribution of the dorsal visual stream to object recognition a group of tertiary students were divided into good and poor motion coherence groups and assessed on tasks classically assumed to rely on ventral stream processing. Participants were required to identify simple line drawings in two tasks, one where objects were presented abruptly for 50 ms followed by a white-noise mask, the other where contrast was linearly ramped on and off over 325 ms and replaced with a mask. Results: Although both groups only differed in motion coherence performance (a dorsal stream measure), the good motion coherence group showed superior contrast sensitivity for object recognition on the abrupt, but not the ramped presentation tasks. Conclusions: We propose that abrupt presentation of objects activated attention mechanisms fed by the dorsal stream, whereas the ramped presentation had reduced transience and thus did not activate dorsal attention mechanisms as well. The results suggest that rapid dorsal stream activation may be required to assist with ventral stream object processing. Background processing of high temporal and low spatial frequencies It is now well established that most visual information at low luminance contrasts, and provides the great projects through the Lateral Geniculate Nucleus (LGN) majority of the contribution to the dorsal stream. The and primary visual cortex (V1) before dividing into two subcortical parvocellular pathway on the other hand has major cortical pathways [1-4]. Firstly, the dorsal stream, been found to be optimally suited to the processing of which is generally accepted to be responsible for motion colour and low temporal and high spatial frequencies at perception, spatial awareness, and vision for action, higher contrast. The parvocellular system mainly pro- includes areas V5, V3a, and V6, and terminates in parie- jects through to the ventral stream, though the magno- tal cortex. Secondly, the ventral stream, which is specia- cellular system also provides a substantial input to the lized for object recognition and includes areas such as ventral stream [2,7,8]. Many experiments have been devoted to understand- the fusiform gyrus and the lateral occipital complex, ter- minates in temporal cortex [4-6]. ing how the dorsal and ventral visual streams interact, These two visual streams are fed by differing ratios of contribute to conscious awareness of visual events, and magnocellular and parvocellular contributions, originat- the ability to make motor responses (e.g., eye- and ing in different laminar layers of the LGN. The magno- hand- movements) [9-14]. cellular pathway is predominantly involved in the One recent model of visual processing, which builds on the work of Bullier [15], proposes that fast subcorti- cal projections of the magnocellular (M) pathway project * Correspondence: r.laycock@latrobe.edu.au through the dorsal stream to initiate exogenously-driven School of Psychological Science, La Trobe University, Melbourne, Australia © 2011 Laycock et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Laycock et al. Behavioral and Brain Functions 2011, 7:34 Page 2 of 7 http://www.behavioralandbrainfunctions.com/content/7/1/34 attention mechanisms in parietal and frontal cortex [16]. for the magnocellular advantage [16]. Levy et al. sug- According to Bullier the earliest information to V5 is gested that poor dorsal stream function may have fed back into V1 in time for the initial parvocellular (P) reduced rapid attention activation in turn impeding the arrivals in V1, and subsequent detailed or more local processing of letter strings through the ventral stream. processing through the ventral stream. This conduction The current study’s aim was to further investigate advantage of the M system over the P system into V1 whether there is early dorsal stream involvement in abrupt onset object recognition. The magnocellular (between 15 and 40 ms in humans) [17-19], leads to the advantage model [16] predicts that abrupt presentation model being termed the ‘magnocellular advantage’ [16]. of salient stimuli will activate dorsal stream-driven exo- A key aspect of this model predicts that rapid activation of frontoparietal attention mechanisms via V5 in the genous attention, to facilitate object-specific ventral dorsal stream plays a preparatory and alerting role to a stream processing. Conversely, if the transient nature of new salient visual event, and assists the fine-detailed the onset/offset of an object is removed - that is, if it processing of object features which occurs later in the does not appear abruptly and rather the onset is gradu- temporal cortex, the termination point of the ventral ally ramped, then the rapid dorsal stream activation of stream. attention mechanisms will not be activated, either at all, The ‘magnocellular advantage’ model has been used to or perhaps as strongly or quickly. Ramped and abrupt explain a range of investigations of visual processing. onset object recognition stimuli have been used pre- For example Laycock and Crewther [20] have argued viously to argue that rapid perception requires transient that a reduction in the magnocellular latency advantage component signalling [31] could interfere with the rapid activation of the parieto- We therefore compared a group of Good and Poor frontal attention network and contribute to understand- motion coherence detectors, created from a normal ing the range of subcortical magnocellular, dorsal population of adults, on an abrupt and a non-abrupt (i.e., stream, and attentional deficiencies reported in develop- ramped) onset/offset match-to-sample object recognition mental dyslexia [21-28]. Laycock et al. [13] have also task, utilising contrast as the dependent variable. Low shown that transcranial magnetic stimulation (TMS) of contrast stimuli are expected to preferentially stimulate areas V1 and V5 in skilled readers leads to an impair- the sub-cortical magnocellular responses, but to require ment in word recognition at different times post word ventral stream processing for successful identification of stimulus onset, arguing for a role for the dorsal stream objects. It was expected that good motion detectors would show superior contrast sensitivity for object recog- in word processing. nition when contrast abruptly reaches its peak contrast Performance on global and local scene segmentation has also been associated with magnocellular pathway when compared with poor motion detectors. integrity [29]. Difficulty in identifying the global compo- When the transient nature of the appearance of the nents of locally salient hierarchical Navon figures has object is removed by gradually increasing the object been associated with higher rather than lower scores on contrast in a linear fashion to a maximum contrast the Autism Quotient (AQ). Sutherland and Crewther (ramped contrast onset) we predict such stimuli will not also showed that the initial cortical response of the mag- be well suited to activating the dorsal stream. Object nocellular afferents was weaker for low contrast stimuli, presentation manipulated to purportedly reduce dorsal and that the magnocellular but not the parvocellular stream activation and parietofrontal attention mechan- pathway demonstrated a delayed response when stimuli isms, was expected to not show any differences between were presented at high contrast, for high compared with good and poor motion coherence detectors. low AQ participants. These findings were suggested to reflect support for impairment in the magnocellular Methods feedback contributions normally apparent in the magno- Participants cellular advantage model [16]. Sixty-two university students participated in the experi- A recent study by Levy, Walsh and Lavidor [30] com- ment. Of these 6 were excluded (see Results section for pared two groups of skilled adult readers, subdivided by details), giving a final sample of 56 (33 female). The performance on a detection of motion coherence task. mean age of participants was 22.39 (SD = 3.89), with a Most importantly for the current purposes, the good rangeof19to34years.All participants hadnormalor motion coherence group showed an advantage in classi- corrected to normal visual acuity, and gave their fying words as real words rather than nonwords. Despite informed consent. all participants being skilled readers, motion coherence performance - a skill requiring dorsal stream processing, Materials predicted rapid visual word identification, a presumed Stimuli were presented on an eMac computer at a view- ventral stream task. These results were taken as support ing distance of 57 cm. The monitor had an 80 Hz Laycock et al. Behavioral and Brain Functions 2011, 7:34 Page 3 of 7 http://www.behavioralandbrainfunctions.com/content/7/1/34 refresh rate, and tasks were programmed and presented one of four possible objects was presented, with the using VPixx software (Version 2.4, http://www.vpixx. same four options (target and three distracters) always com). Participants also completed the Ravens Standard presented. The two staircase procedures were interwo- Progressive Matrices [32], which is a measure of non- ven with each other such that each of the eight objects verbal mentation whereby participants have 20 minutes was presented in random order. The mean of the two to complete as many of the visual puzzles as possible in resulting thresholds was used for data analysis. Inspec- order to confirm that participants did not differ in gen- tion of raw data indicated that no participants reached a eral nonverbal intelligence. ceiling level, performing well below the lowest possible contrast. Motion Coherence Detection Task Two hundred white dots (5 pixels (0.17 deg at 57 cm) high and wide) were placed within an illusory square Procedure subtending 7.5° by 7.5° on a black background. A per- Participants first completed the Ravens task, followed by, centage of the dots moved coherently in one direction in counterbalanced order, the Motion Coherence detec- across the square whilst the remaining dots moved in tion and two Object Recognition tasks. Participants also random directions. All dots had a speed of 4 pixels per completed a reading test and another visual psychophysics frame (11.3 deg/s at 57 cm), and a limited lifetime of task as part of another project. The entire testing session 200 ms. A blank screen appeared for 500 ms followed duration was 1 hour. During the visual tasks participants by the motion stimulus for a further 500 ms, before sat in a darkened room. The visual task order was rando- being replaced by a black screen. Coherent dot direction mised between participants. Before each task began, an could be in one of four directions (up, down, left, right) experimenter explained the task and gave demonstrations and participants were requiredtoindicateviaakey of trials until the participant understood the task. press the perceived direction of coherent dots in a four- alternate forced-choice design. The level of coherence Results was adjusted in a staircase procedure, which terminated Object recognition contrast thresholds from 5 partici- after 10 reversals. Step size was 5%, and then 3% after pants were unreliable due to failed staircase procedures, the first reversal. The threshold coherence level was with a further participant showing inconsistent motion taken as the mean of the final 6 reversals. coherence thresholds in repeated runs. These 6 partici- Abrupt and Ramped Onset Object Recognition Tasks pants were thus excluded and reduced our sample to 56. One of eight line drawings of easily recognizable objects An initial correlation analysis demonstrated a poor (e.g., clock, iron, teacup) were presented to participants linear relationship between Motion Coherence and in the middle of the screen, subtending between 8-10° Abrupt Object Recognition (r = .006, p =.96), andalso by 8-10°. In the Abrupt contrast onset/offset task objects between Motion Coherence and Ramped Object Recog- appeared at a constant contrast between foreground and nition (r =-.119, p = .37). Given the nonlinear relation- background for four computer-refresh frames (50 ms). ship between Motion Coherence and Abrupt Object In the Ramped contrast onset/offset task, object contrast recognition, participant thresholds for the Motion was ramped in a linear fashion, increasing from 0% to a Coherence task were ranked, and the top and bottom maximum (over 13 frames), before reducing back to 0% thirds were categorized as the Good and Poor Motion contrast (over 13 frames), giving a total object duration Coherence (MC) groups, respectively.Asisseen in of 325 ms. In both tasks, target objects were replaced by Figure 1, this method was successful in creating two dis- a rectangular white-noise mask (subtending 9° by 9°). tinct subgroups, which differed significantly in their Participants were then presented with four objects (the motion coherence abilities (Good MC: mean threshold target, and three distracter line drawing objects), and =23%, n = 18, CI [22,25]; Poor MC: mean threshold = were asked to identify with a keyboard press the target 47%, n = 18, CI [43,50], t(36) = 12.1, p < .0001). These object, in a four-alternate force-choice match-to-sample thresholds are slightly higher than previously found [33], paradigm. All distracters also appeared as targets in though this is likely to be explained by the short dura- other trials, and no feedback was provided to the parti- tion of the stimulus (500 ms) and the limited lifetime of cipant during the task. the dots (200 ms) giving a threshold in accordance with Threshold contrast was determined by use of a stair- the results from Sutherland and Crewther [29] who case procedure by adjusting the percent contrast. The used more similar parameters. staircase terminated after 10 reversals and threshold was In order to test whether Good and Poor MC groups taken as the mean contrast level from the final 6 rever- differed in some attribute other than motion coherence sals. The eight objects were split into two halves with a detection, groups were compared on the Ravens Pro- separate staircase procedure conducted on each group gressive Matrices, and demonstrated no significant dif- of objects. This meant that within each staircase only ference (t(34) = 0.18, p = .86). Laycock et al. Behavioral and Brain Functions 2011, 7:34 Page 4 of 7 http://www.behavioralandbrainfunctions.com/content/7/1/34 60.00 50.00 40.00 30.00 20.00 10.00 Figure 3 Motion Coherence (MC) groups’ Ramped object recognition performance. Bar graph shows mean contrast threshold (± SE) for the Good compared with the Poor MC groups, Good MC Group Middle MC Group Poor MC group and the Middle MC group also shown, on the Object recognition Motion Coherence (MC) Groups task with ramped presentation. The Good and Poor MC groups Figure 1 Motion coherence detection thresholds for different demonstrated equal contrast threshold (p > .05). Motion Coherence (MC) groups. Box plots showing the distribution of the three motion coherence groups, created by taking the top, middle and bottom third of ranked threshold scores. showing no significant difference (t(34) = 0.76, p = .45). Similarly, Figure 3 also shows the performance of the Finally, we compared the two subgroups of Motion middle MC group is comparable with the Poor MC Coherence abilities on the Abrupt and Ramped Object group (p = .91) Recognition tasks. Figure 2 illustrates that the Good MC group demonstrated a lower mean contrast threshold Discussion than the Poor MC group on the Abrupt contrast onset/ The current study investigated the contribution of dor- offset task. A t-test confirmed that the two groups dif- sal stream functioning in object recognition. This was fered significantly on the Abrupt task (t(34) = 2.10, p = achieved by manipulating the degree to which line- .04, d = 0.70). Figure 2 also shows that the performance drawings of objects appeared suddenly or not by includ- of the middle MC group is comparable with the Poor ing abrupt and ramped onset tasks, and comparing two MC group (p = .82) On the other hand, as can be seen subgroups presumed to differ only in their performance in Figure 3, Good and Poor MC groups showed very on motion coherence ability - a task considered to be similar contrast thresholds for the Ramped contrast representative of dorsal stream functioning. onset/offset task, with a t-test comparing groups The two subgroups of motion coherence ability were only found to differ on an object recognition task when the objects had a relatively stronger attention-grabbing sudden appearance (i.e., objects appeared abruptly), and presumed to therefore more strongly activate bottom-up attention mechanisms in parietal cortex. It is suggested however, that Good and Poor MC groups did not differ in object specific processing per se. When the transient nature of the onset/offset of the object was reduced, by gradually ramping the contrast between foreground and background, the good and poor motion coherence groups showed comparable performance. We propose that the only difference between the two object recogni- tion tasks relates to the physical presentation of the objects. In particular, our tasks differed in two ways: the Figure 2 Motion Coherence (MC) groups’ Abrupt object nature of the onset, and the duration of the presentation recognition performance. Bar graph shows mean contrast of the target object (see further discussion of this below) threshold (± SE) for the Good compared with the Poor MC groups, and the Middle MC group also shown, on the Object recognition rather than the objects themselves. task with abrupt presentation. The Good MC group showed Given that the two subgroups showed equal nonverbal significantly superior contrast threshold than the Poor MC group mentation, and therefore no differences in general atten- (p < .05). tion or motivation, but differed only in their motion Percent (%) Motion Coherence Threshold ! Laycock et al. Behavioral and Brain Functions 2011, 7:34 Page 5 of 7 http://www.behavioralandbrainfunctions.com/content/7/1/34 coherence ability, we suggest that relatively reduced dor- initiate parietal attention mechanisms, the results may sal stream functioning may help explain the differential have more to do with difference between stimuli in tem- object recognition performance with abrupt compared poral frequencies. It is possible that the abrupt stimuli with ramped onset/offset stimuli. This would appear were more efficient than ramped stimuli at activating consistent with Levy et al. [30] who showed that good high temporal frequency processing, likely to be handled motion coherence detectors were better at classifying by the magnocellular pathway. Thus, it may be that the abrupt stimuli activate a fast magnocellular response (in words as real words rather than nonwords compared the Good MC, but not the Poor MC group), which is with poor motion coherence detectors. In both Levy et most likely fed through the dorsal stream [1,4]. On the al. and in the current study, skills known to require acti- vation of ventral extrastriate cortex (reading and object other hand, the ramped task, consisting of the longer recognition, respectively) were found to be related to duration, and thus creating a slower temporal frequency proficiency in a known dorsal stream task (detection of would be less suited to activating early magnocellular motion coherence). processing in LGN. Such stimuli might be expected to A possible explanation for the current findings relies rely less on the magnocellular advantage, with both MC on the magnocellular advantage model of visual proces- groups therefore having to rely primarily on ventral sing [16] in which the rapid onset of stimuli is proposed stream processing. to activate the largely magnocellular dorsal visual stream Thefinding ofa rolefor thedorsalstream in object and to initiate visual attention mechanisms in parietal recognition requires mention of previous experiments cortex. Rapid feedback to primary visual cortex, but suggesting that the dorsal stream is involved in proces- potentially also horizontal connections from dorsal to sing of specific categories of objects. Goodale and Mil- ventral regions, or parietal to frontal connections fol- ner [5,12] have proposed a dichotomy whereby the lowed by feedback to ventral stream regions may all ventral stream handles vision for perception, whilst the contribute to a detailed analysis of the visual scene. The dorsal stream is a non-conscious vision for action path- key aspect of this model for the current study relates to way. Fang and He [36] have shown with fMRI that the the rapid activation of parietal attention mechanisms by dorsal stream (functionally defined by the authors as V5 and the dorsal stream - which are predicted to not areas corresponding to V3a/V7) still responded to a be activated for visual stimuli with reduced salience (i.e., diverse range of object images rendered invisible by the ramped presentation in this study). interocular suppression, but this effect was stronger in “tools” than faces. Other findings using similar para- Such a model is supported by the work of Bar and digms have suggested that the dorsal stream influences colleagues who have used MEG to show that low spatial frequency visual information (i.e., magnocellular-type ventral stream processing of manipulable objects (e.g., information) is projected through the dorsal stream to tools) [37,38]. reach orbitofrontal cortex by approximately 130 ms, and Although most of the objects used in the current then fusiform gyrus in the ventral stream 50 ms later study might be considered manipulable (e.g., iron, tea- [34]. Bar et al. argued that the dorsal stream projection cup), we suggest that our results cannot be interpreted to parietal and frontal cortices provides a course repre- as evidence for dorsal stream involvement in the recog- sentation of the object, and triggers a top-down facilita- nition of objects, which are manipulable as compared to tion of detailed object processing into temporal cortex. other non-manipulable objects (e.g., words), and there- This is similar to an “attentional spotlight” model utilis- fore cannot address the vision for action theory directly. ing parietal mechanisms to guide temporal cortex pro- This is due to the finding that although our participant cessing [35]. However this model focuses more on groups (split on a measure of dorsal stream processing) spatial attention shifts, whereas the magnocellular differed on a measure of object recognition (of poten- advantage model [16] allows for rapid activation of tially manipulable objects) they did not show different attention directed to objects within central fixation well- performance when we adjusted the presentation format, suited to the magnocellular system (i.e., low spatial fre- but used the exact same objects. That is, it does not quency, flickering, rapid or moving salient stimuli) to be appear that the influence of dorsal stream ability on used to initiate attention and/or higher cognitive pro- object recognition is related to the type of object, but is cesses and to facilitate later detailed processing in tem- more likely related to the visual attributes (i.e., the nat- poral cortex. ure of the onset/offsets) of these objects. Furthermore, there is a large literature that has argued Given that the stimuli in the two tasks differed in the that the dorsal stream is involved in object recognition total duration (50 ms and 325 ms for abrupt and unrelated to action or the manipulation of objects. For ramped objects, respectively), an alternative explanation may be posited. Rather than the presence or absence of example previous work has demonstrated dorsal stream an abrupt onset/offset activating the dorsal stream to involvement in word recognition [13,27,30,34]. The Laycock et al. Behavioral and Brain Functions 2011, 7:34 Page 6 of 7 http://www.behavioralandbrainfunctions.com/content/7/1/34 4. Nassi JJ, Callaway EM: Parallel processing strategies of the primate visual likely role of the dorsal stream in this type of non- system. Nat Rev Neurosci 2009, 10:360-372. manipulable object processing is likely to be in initiating 5. Goodale MA, Milner AD: Separate visual pathways for perception and frontoparietal attention mechanisms and in facilitating action. Trends Neurosci 1992, 15:20-25. 6. Haxby JV, Grady CL, Horwitz B, Ungerleider LG, Mishkin M, Carson RE, top-down facilitation of ventral stream object proces- Herscovitch P, Schapiro MB, Rapoport SI: Dissociation of object and spatial sing. Bar et al [34], for example, provided MEG evidence visual processing pathways in human extrastriate cortex. Proc Natl Acad that an early magnocellular projection through the dor- Sci USA 1991, 88:1621-1625. 7. Kaplan E, Shapley RM: X and Y cells in the lateral geniculate nucleus of sal stream activated orbitofrontal cortex and was fol- macaque monkeys. J Physiol 1982, 330:125-143. lowed by a later ventral stream (fusiform) activation for 8. Schiller PH, Logothetis NK: The color-opponent and broad-band channels objects(e.g.,tools,furniture,clothes,animals,meansof of the primate visual system. Trends Neurosci 1990, 13:392-398. 9. Chen CM, Lakatos P, Shah AS, Mehta AD, Givre SJ, Javitt DC, Schroeder CE: transportation). Functional anatomy and interaction of fast and slow visual pathways in macaque monkeys. Cereb Cortex 2007, 17:1561-1569. Conclusions 10. Ellison A, Cowey A: Time course of the involvement of the ventral and dorsal visual processing streams in a visuospatial task. Neuropsychologia The current data cannot establish a causal relationship 2007, 45:3335-3339. between dorsal stream functioning (as assessed by 11. Foxe JJ, Simpson GV: Flow of activation from V1 to frontal cortex in motion coherence performance) and relatively more or humans: a framework for defining “early” visual processing. Exp Brain Res 2002, 142:139-150. less transient onset/offset object recognition. As alluded 12. Goodale MA: Action without perception in human vision. Cogn to earlier Laycock et al. [13] used TMS to disrupt V1/ Neuropsychol 2008, 25:891-919. V2 and V5 in a word recognition task. Reduced single 13. Laycock R, Crewther DP, Fitzgerald PB, Crewther SG: TMS disruption of V5/ MT+ indicates a role for the dorsal stream in word recognition. Exp Brain (abruptonset)wordidentificationfollowing TMS Res 2009, 197:69-79. induced disruption of V5 argues for a causal role of the 14. Livingstone MS, Hubel DH: Psychophysical evidence for separate dorsal stream in rapid accurate (fluent) reading. TMS channels for the perception of form, color, movement, and depth. J Neurosci 1987, 7:3416-3468. provides the opportunity to further explore the neces- 15. Bullier J: Integrated model of visual processing. Brain Res Brain Res Rev sary role of dorsal and ventral visual regions in object 2001, 36:96-107. recognition while allowing the mapping of the temporal 16. Laycock R, Crewther SG, Crewther DP: A role for the ‘magnocellular advantage’ in visual impairments in neurodevelopmental and psychiatric order of events within early dorsal, parietal and ventral disorders. Neurosci Biobehav Rev 2007, 31:363-376. regions. Nevertheless, this psychophysical experiment 17. Klistorner A, Crewther DP, Crewther SG: Separate magnocellular and has produced further evidence that the dorsal stream is parvocellular contributions from temporal analysis of the multifocal VEP. Vision Res 1997, 37:2161-2169. required for detection of abrupt but not for ramped 18. Paulus W, Korinth S, Wischer S, Tergau F: Differential inhibition of onset/offset objects discrimination. chromatic and achromatic perception by transcranial magnetic stimulation of the human visual cortex. Neuroreport 1999, 10:1245-1248. 19. Baseler HA, Sutter EE: M and P components of the VEP and their visual Acknowledgements field distribution. Vision Res 1997, 37:675-690. This research was supported by Australian Research Council grant 20. Laycock R, Crewther SG: Towards an understanding of the role of the DP0985837 to the last author, and by funds to the first author. Thanks to ‘magnocellular advantage’ in fluent reading. Neurosci Biobehav Rev 2008, Janelle Christmas, Lucia Colla, Sawsan Hassan, Jude Jayasuriya, and Courtney 32:1494-1506. Shiels for their help with data collection. 21. Borsting E, Ridder WH, Dudeck K, Kelley C, Matsui L, Motoyama J: The presence of a magnocellular defect depends on the type of dyslexia. Authors’ contributions Vision Res 1996, 36:1047-1053. RL conceived of the study and participated in it’s design and coordination, 22. Cornelissen PL, Hansen PC, Gilchrist I, Cormack F, Essex J, Frankish C: designed visual stimuli, and helped to draft the manuscript. AJC helped with Coherent motion detection and letter position encoding. Vision Res 1998, study design and data collection. TL helped with study design and data 38:2181-2191. collection. SGC conceived of the study, and participated in its design, and 23. Demb JB, Boynton GM, Best M, Heeger DJ: Psychophysical evidence for a helped to draft the manuscript. All authors read and approved the magnocellular pathway deficit in dyslexia. Vision Res 1998, 38:1555-1559. manuscript. 24. Hari R, Renvall H, Tanskanen T: Left minineglect in dyslexic adults. Brain 2001, 124:1373-1380. Competing interests 25. Iles J, Walsh V, Richardson A: Visual search performance in dyslexia. The authors declare that they have no competing interests. Dyslexia 2000, 6:163-177. 26. Martin F, Lovegrove WJ: Uniform-field flicker masking in control and Received: 15 March 2011 Accepted: 16 August 2011 specifically-disabled readers. Perception 1988, 17:203-214. Published: 16 August 2011 27. Pammer K, Hansen P, Holliday I, Cornelissen P: Attentional shifting and the role of the dorsal pathway in visual word recognition. Neuropsychologia 2006, 44:2926-2936. References 28. Lovegrove W, Martin F, Bowling A, Blackwood M, Badcock D, Paxton S: 1. Maunsell JH, Nealey TA, DePriest DD: Magnocellular and parvocellular Contrast sensitivity functions and specific reading disability. contributions to responses in the middle temporal visual area (MT) of Neuropsychologia 1982, 20:309-315. the macaque monkey. J Neurosci 1990, 10:3323-3334. 29. Sutherland A, Crewther DP: Magnocellular visual evoked potential delay 2. Merigan WH, Katz LM, Maunsell JH: The effects of parvocellular lateral with high autism spectrum quotient yields a neural mechanism for geniculate lesions on the acuity and contrast sensitivity of macaque altered perception. Brain 2010, 133:2089-2097. monkeys. J Neurosci 1991, 11:994-1001. 30. Levy T, Walsh V, Lavidor M: Dorsal stream modulation of visual word 3. Merigan WH, Maunsell JH: How parallel are the primate visual pathways? recognition in skilled readers. Vision Res 2010, 50:883-888. 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Dorsal stream involvement in recognition of objects with transient onset but not with ramped onset

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Copyright © 2011 by Laycock et al; licensee BioMed Central Ltd.
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Biomedicine; Neurosciences; Neurology; Behavioral Therapy; Psychiatry
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Abstract

Background: Although the ventral visual stream is understood to be responsible for object recognition, it has been proposed that the dorsal stream may contribute to object recognition by rapidly activating parietal attention mechanisms, prior to ventral stream object processing. Methods: To investigate the relative contribution of the dorsal visual stream to object recognition a group of tertiary students were divided into good and poor motion coherence groups and assessed on tasks classically assumed to rely on ventral stream processing. Participants were required to identify simple line drawings in two tasks, one where objects were presented abruptly for 50 ms followed by a white-noise mask, the other where contrast was linearly ramped on and off over 325 ms and replaced with a mask. Results: Although both groups only differed in motion coherence performance (a dorsal stream measure), the good motion coherence group showed superior contrast sensitivity for object recognition on the abrupt, but not the ramped presentation tasks. Conclusions: We propose that abrupt presentation of objects activated attention mechanisms fed by the dorsal stream, whereas the ramped presentation had reduced transience and thus did not activate dorsal attention mechanisms as well. The results suggest that rapid dorsal stream activation may be required to assist with ventral stream object processing. Background processing of high temporal and low spatial frequencies It is now well established that most visual information at low luminance contrasts, and provides the great projects through the Lateral Geniculate Nucleus (LGN) majority of the contribution to the dorsal stream. The and primary visual cortex (V1) before dividing into two subcortical parvocellular pathway on the other hand has major cortical pathways [1-4]. Firstly, the dorsal stream, been found to be optimally suited to the processing of which is generally accepted to be responsible for motion colour and low temporal and high spatial frequencies at perception, spatial awareness, and vision for action, higher contrast. The parvocellular system mainly pro- includes areas V5, V3a, and V6, and terminates in parie- jects through to the ventral stream, though the magno- tal cortex. Secondly, the ventral stream, which is specia- cellular system also provides a substantial input to the lized for object recognition and includes areas such as ventral stream [2,7,8]. Many experiments have been devoted to understand- the fusiform gyrus and the lateral occipital complex, ter- minates in temporal cortex [4-6]. ing how the dorsal and ventral visual streams interact, These two visual streams are fed by differing ratios of contribute to conscious awareness of visual events, and magnocellular and parvocellular contributions, originat- the ability to make motor responses (e.g., eye- and ing in different laminar layers of the LGN. The magno- hand- movements) [9-14]. cellular pathway is predominantly involved in the One recent model of visual processing, which builds on the work of Bullier [15], proposes that fast subcorti- cal projections of the magnocellular (M) pathway project * Correspondence: r.laycock@latrobe.edu.au through the dorsal stream to initiate exogenously-driven School of Psychological Science, La Trobe University, Melbourne, Australia © 2011 Laycock et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Laycock et al. Behavioral and Brain Functions 2011, 7:34 Page 2 of 7 http://www.behavioralandbrainfunctions.com/content/7/1/34 attention mechanisms in parietal and frontal cortex [16]. for the magnocellular advantage [16]. Levy et al. sug- According to Bullier the earliest information to V5 is gested that poor dorsal stream function may have fed back into V1 in time for the initial parvocellular (P) reduced rapid attention activation in turn impeding the arrivals in V1, and subsequent detailed or more local processing of letter strings through the ventral stream. processing through the ventral stream. This conduction The current study’s aim was to further investigate advantage of the M system over the P system into V1 whether there is early dorsal stream involvement in abrupt onset object recognition. The magnocellular (between 15 and 40 ms in humans) [17-19], leads to the advantage model [16] predicts that abrupt presentation model being termed the ‘magnocellular advantage’ [16]. of salient stimuli will activate dorsal stream-driven exo- A key aspect of this model predicts that rapid activation of frontoparietal attention mechanisms via V5 in the genous attention, to facilitate object-specific ventral dorsal stream plays a preparatory and alerting role to a stream processing. Conversely, if the transient nature of new salient visual event, and assists the fine-detailed the onset/offset of an object is removed - that is, if it processing of object features which occurs later in the does not appear abruptly and rather the onset is gradu- temporal cortex, the termination point of the ventral ally ramped, then the rapid dorsal stream activation of stream. attention mechanisms will not be activated, either at all, The ‘magnocellular advantage’ model has been used to or perhaps as strongly or quickly. Ramped and abrupt explain a range of investigations of visual processing. onset object recognition stimuli have been used pre- For example Laycock and Crewther [20] have argued viously to argue that rapid perception requires transient that a reduction in the magnocellular latency advantage component signalling [31] could interfere with the rapid activation of the parieto- We therefore compared a group of Good and Poor frontal attention network and contribute to understand- motion coherence detectors, created from a normal ing the range of subcortical magnocellular, dorsal population of adults, on an abrupt and a non-abrupt (i.e., stream, and attentional deficiencies reported in develop- ramped) onset/offset match-to-sample object recognition mental dyslexia [21-28]. Laycock et al. [13] have also task, utilising contrast as the dependent variable. Low shown that transcranial magnetic stimulation (TMS) of contrast stimuli are expected to preferentially stimulate areas V1 and V5 in skilled readers leads to an impair- the sub-cortical magnocellular responses, but to require ment in word recognition at different times post word ventral stream processing for successful identification of stimulus onset, arguing for a role for the dorsal stream objects. It was expected that good motion detectors would show superior contrast sensitivity for object recog- in word processing. nition when contrast abruptly reaches its peak contrast Performance on global and local scene segmentation has also been associated with magnocellular pathway when compared with poor motion detectors. integrity [29]. Difficulty in identifying the global compo- When the transient nature of the appearance of the nents of locally salient hierarchical Navon figures has object is removed by gradually increasing the object been associated with higher rather than lower scores on contrast in a linear fashion to a maximum contrast the Autism Quotient (AQ). Sutherland and Crewther (ramped contrast onset) we predict such stimuli will not also showed that the initial cortical response of the mag- be well suited to activating the dorsal stream. Object nocellular afferents was weaker for low contrast stimuli, presentation manipulated to purportedly reduce dorsal and that the magnocellular but not the parvocellular stream activation and parietofrontal attention mechan- pathway demonstrated a delayed response when stimuli isms, was expected to not show any differences between were presented at high contrast, for high compared with good and poor motion coherence detectors. low AQ participants. These findings were suggested to reflect support for impairment in the magnocellular Methods feedback contributions normally apparent in the magno- Participants cellular advantage model [16]. Sixty-two university students participated in the experi- A recent study by Levy, Walsh and Lavidor [30] com- ment. Of these 6 were excluded (see Results section for pared two groups of skilled adult readers, subdivided by details), giving a final sample of 56 (33 female). The performance on a detection of motion coherence task. mean age of participants was 22.39 (SD = 3.89), with a Most importantly for the current purposes, the good rangeof19to34years.All participants hadnormalor motion coherence group showed an advantage in classi- corrected to normal visual acuity, and gave their fying words as real words rather than nonwords. Despite informed consent. all participants being skilled readers, motion coherence performance - a skill requiring dorsal stream processing, Materials predicted rapid visual word identification, a presumed Stimuli were presented on an eMac computer at a view- ventral stream task. These results were taken as support ing distance of 57 cm. The monitor had an 80 Hz Laycock et al. Behavioral and Brain Functions 2011, 7:34 Page 3 of 7 http://www.behavioralandbrainfunctions.com/content/7/1/34 refresh rate, and tasks were programmed and presented one of four possible objects was presented, with the using VPixx software (Version 2.4, http://www.vpixx. same four options (target and three distracters) always com). Participants also completed the Ravens Standard presented. The two staircase procedures were interwo- Progressive Matrices [32], which is a measure of non- ven with each other such that each of the eight objects verbal mentation whereby participants have 20 minutes was presented in random order. The mean of the two to complete as many of the visual puzzles as possible in resulting thresholds was used for data analysis. Inspec- order to confirm that participants did not differ in gen- tion of raw data indicated that no participants reached a eral nonverbal intelligence. ceiling level, performing well below the lowest possible contrast. Motion Coherence Detection Task Two hundred white dots (5 pixels (0.17 deg at 57 cm) high and wide) were placed within an illusory square Procedure subtending 7.5° by 7.5° on a black background. A per- Participants first completed the Ravens task, followed by, centage of the dots moved coherently in one direction in counterbalanced order, the Motion Coherence detec- across the square whilst the remaining dots moved in tion and two Object Recognition tasks. Participants also random directions. All dots had a speed of 4 pixels per completed a reading test and another visual psychophysics frame (11.3 deg/s at 57 cm), and a limited lifetime of task as part of another project. The entire testing session 200 ms. A blank screen appeared for 500 ms followed duration was 1 hour. During the visual tasks participants by the motion stimulus for a further 500 ms, before sat in a darkened room. The visual task order was rando- being replaced by a black screen. Coherent dot direction mised between participants. Before each task began, an could be in one of four directions (up, down, left, right) experimenter explained the task and gave demonstrations and participants were requiredtoindicateviaakey of trials until the participant understood the task. press the perceived direction of coherent dots in a four- alternate forced-choice design. The level of coherence Results was adjusted in a staircase procedure, which terminated Object recognition contrast thresholds from 5 partici- after 10 reversals. Step size was 5%, and then 3% after pants were unreliable due to failed staircase procedures, the first reversal. The threshold coherence level was with a further participant showing inconsistent motion taken as the mean of the final 6 reversals. coherence thresholds in repeated runs. These 6 partici- Abrupt and Ramped Onset Object Recognition Tasks pants were thus excluded and reduced our sample to 56. One of eight line drawings of easily recognizable objects An initial correlation analysis demonstrated a poor (e.g., clock, iron, teacup) were presented to participants linear relationship between Motion Coherence and in the middle of the screen, subtending between 8-10° Abrupt Object Recognition (r = .006, p =.96), andalso by 8-10°. In the Abrupt contrast onset/offset task objects between Motion Coherence and Ramped Object Recog- appeared at a constant contrast between foreground and nition (r =-.119, p = .37). Given the nonlinear relation- background for four computer-refresh frames (50 ms). ship between Motion Coherence and Abrupt Object In the Ramped contrast onset/offset task, object contrast recognition, participant thresholds for the Motion was ramped in a linear fashion, increasing from 0% to a Coherence task were ranked, and the top and bottom maximum (over 13 frames), before reducing back to 0% thirds were categorized as the Good and Poor Motion contrast (over 13 frames), giving a total object duration Coherence (MC) groups, respectively.Asisseen in of 325 ms. In both tasks, target objects were replaced by Figure 1, this method was successful in creating two dis- a rectangular white-noise mask (subtending 9° by 9°). tinct subgroups, which differed significantly in their Participants were then presented with four objects (the motion coherence abilities (Good MC: mean threshold target, and three distracter line drawing objects), and =23%, n = 18, CI [22,25]; Poor MC: mean threshold = were asked to identify with a keyboard press the target 47%, n = 18, CI [43,50], t(36) = 12.1, p < .0001). These object, in a four-alternate force-choice match-to-sample thresholds are slightly higher than previously found [33], paradigm. All distracters also appeared as targets in though this is likely to be explained by the short dura- other trials, and no feedback was provided to the parti- tion of the stimulus (500 ms) and the limited lifetime of cipant during the task. the dots (200 ms) giving a threshold in accordance with Threshold contrast was determined by use of a stair- the results from Sutherland and Crewther [29] who case procedure by adjusting the percent contrast. The used more similar parameters. staircase terminated after 10 reversals and threshold was In order to test whether Good and Poor MC groups taken as the mean contrast level from the final 6 rever- differed in some attribute other than motion coherence sals. The eight objects were split into two halves with a detection, groups were compared on the Ravens Pro- separate staircase procedure conducted on each group gressive Matrices, and demonstrated no significant dif- of objects. This meant that within each staircase only ference (t(34) = 0.18, p = .86). Laycock et al. Behavioral and Brain Functions 2011, 7:34 Page 4 of 7 http://www.behavioralandbrainfunctions.com/content/7/1/34 60.00 50.00 40.00 30.00 20.00 10.00 Figure 3 Motion Coherence (MC) groups’ Ramped object recognition performance. Bar graph shows mean contrast threshold (± SE) for the Good compared with the Poor MC groups, Good MC Group Middle MC Group Poor MC group and the Middle MC group also shown, on the Object recognition Motion Coherence (MC) Groups task with ramped presentation. The Good and Poor MC groups Figure 1 Motion coherence detection thresholds for different demonstrated equal contrast threshold (p > .05). Motion Coherence (MC) groups. Box plots showing the distribution of the three motion coherence groups, created by taking the top, middle and bottom third of ranked threshold scores. showing no significant difference (t(34) = 0.76, p = .45). Similarly, Figure 3 also shows the performance of the Finally, we compared the two subgroups of Motion middle MC group is comparable with the Poor MC Coherence abilities on the Abrupt and Ramped Object group (p = .91) Recognition tasks. Figure 2 illustrates that the Good MC group demonstrated a lower mean contrast threshold Discussion than the Poor MC group on the Abrupt contrast onset/ The current study investigated the contribution of dor- offset task. A t-test confirmed that the two groups dif- sal stream functioning in object recognition. This was fered significantly on the Abrupt task (t(34) = 2.10, p = achieved by manipulating the degree to which line- .04, d = 0.70). Figure 2 also shows that the performance drawings of objects appeared suddenly or not by includ- of the middle MC group is comparable with the Poor ing abrupt and ramped onset tasks, and comparing two MC group (p = .82) On the other hand, as can be seen subgroups presumed to differ only in their performance in Figure 3, Good and Poor MC groups showed very on motion coherence ability - a task considered to be similar contrast thresholds for the Ramped contrast representative of dorsal stream functioning. onset/offset task, with a t-test comparing groups The two subgroups of motion coherence ability were only found to differ on an object recognition task when the objects had a relatively stronger attention-grabbing sudden appearance (i.e., objects appeared abruptly), and presumed to therefore more strongly activate bottom-up attention mechanisms in parietal cortex. It is suggested however, that Good and Poor MC groups did not differ in object specific processing per se. When the transient nature of the onset/offset of the object was reduced, by gradually ramping the contrast between foreground and background, the good and poor motion coherence groups showed comparable performance. We propose that the only difference between the two object recogni- tion tasks relates to the physical presentation of the objects. In particular, our tasks differed in two ways: the Figure 2 Motion Coherence (MC) groups’ Abrupt object nature of the onset, and the duration of the presentation recognition performance. Bar graph shows mean contrast of the target object (see further discussion of this below) threshold (± SE) for the Good compared with the Poor MC groups, and the Middle MC group also shown, on the Object recognition rather than the objects themselves. task with abrupt presentation. The Good MC group showed Given that the two subgroups showed equal nonverbal significantly superior contrast threshold than the Poor MC group mentation, and therefore no differences in general atten- (p < .05). tion or motivation, but differed only in their motion Percent (%) Motion Coherence Threshold ! Laycock et al. Behavioral and Brain Functions 2011, 7:34 Page 5 of 7 http://www.behavioralandbrainfunctions.com/content/7/1/34 coherence ability, we suggest that relatively reduced dor- initiate parietal attention mechanisms, the results may sal stream functioning may help explain the differential have more to do with difference between stimuli in tem- object recognition performance with abrupt compared poral frequencies. It is possible that the abrupt stimuli with ramped onset/offset stimuli. This would appear were more efficient than ramped stimuli at activating consistent with Levy et al. [30] who showed that good high temporal frequency processing, likely to be handled motion coherence detectors were better at classifying by the magnocellular pathway. Thus, it may be that the abrupt stimuli activate a fast magnocellular response (in words as real words rather than nonwords compared the Good MC, but not the Poor MC group), which is with poor motion coherence detectors. In both Levy et most likely fed through the dorsal stream [1,4]. On the al. and in the current study, skills known to require acti- vation of ventral extrastriate cortex (reading and object other hand, the ramped task, consisting of the longer recognition, respectively) were found to be related to duration, and thus creating a slower temporal frequency proficiency in a known dorsal stream task (detection of would be less suited to activating early magnocellular motion coherence). processing in LGN. Such stimuli might be expected to A possible explanation for the current findings relies rely less on the magnocellular advantage, with both MC on the magnocellular advantage model of visual proces- groups therefore having to rely primarily on ventral sing [16] in which the rapid onset of stimuli is proposed stream processing. to activate the largely magnocellular dorsal visual stream Thefinding ofa rolefor thedorsalstream in object and to initiate visual attention mechanisms in parietal recognition requires mention of previous experiments cortex. Rapid feedback to primary visual cortex, but suggesting that the dorsal stream is involved in proces- potentially also horizontal connections from dorsal to sing of specific categories of objects. Goodale and Mil- ventral regions, or parietal to frontal connections fol- ner [5,12] have proposed a dichotomy whereby the lowed by feedback to ventral stream regions may all ventral stream handles vision for perception, whilst the contribute to a detailed analysis of the visual scene. The dorsal stream is a non-conscious vision for action path- key aspect of this model for the current study relates to way. Fang and He [36] have shown with fMRI that the the rapid activation of parietal attention mechanisms by dorsal stream (functionally defined by the authors as V5 and the dorsal stream - which are predicted to not areas corresponding to V3a/V7) still responded to a be activated for visual stimuli with reduced salience (i.e., diverse range of object images rendered invisible by the ramped presentation in this study). interocular suppression, but this effect was stronger in “tools” than faces. Other findings using similar para- Such a model is supported by the work of Bar and digms have suggested that the dorsal stream influences colleagues who have used MEG to show that low spatial frequency visual information (i.e., magnocellular-type ventral stream processing of manipulable objects (e.g., information) is projected through the dorsal stream to tools) [37,38]. reach orbitofrontal cortex by approximately 130 ms, and Although most of the objects used in the current then fusiform gyrus in the ventral stream 50 ms later study might be considered manipulable (e.g., iron, tea- [34]. Bar et al. argued that the dorsal stream projection cup), we suggest that our results cannot be interpreted to parietal and frontal cortices provides a course repre- as evidence for dorsal stream involvement in the recog- sentation of the object, and triggers a top-down facilita- nition of objects, which are manipulable as compared to tion of detailed object processing into temporal cortex. other non-manipulable objects (e.g., words), and there- This is similar to an “attentional spotlight” model utilis- fore cannot address the vision for action theory directly. ing parietal mechanisms to guide temporal cortex pro- This is due to the finding that although our participant cessing [35]. However this model focuses more on groups (split on a measure of dorsal stream processing) spatial attention shifts, whereas the magnocellular differed on a measure of object recognition (of poten- advantage model [16] allows for rapid activation of tially manipulable objects) they did not show different attention directed to objects within central fixation well- performance when we adjusted the presentation format, suited to the magnocellular system (i.e., low spatial fre- but used the exact same objects. That is, it does not quency, flickering, rapid or moving salient stimuli) to be appear that the influence of dorsal stream ability on used to initiate attention and/or higher cognitive pro- object recognition is related to the type of object, but is cesses and to facilitate later detailed processing in tem- more likely related to the visual attributes (i.e., the nat- poral cortex. ure of the onset/offsets) of these objects. Furthermore, there is a large literature that has argued Given that the stimuli in the two tasks differed in the that the dorsal stream is involved in object recognition total duration (50 ms and 325 ms for abrupt and unrelated to action or the manipulation of objects. For ramped objects, respectively), an alternative explanation may be posited. Rather than the presence or absence of example previous work has demonstrated dorsal stream an abrupt onset/offset activating the dorsal stream to involvement in word recognition [13,27,30,34]. The Laycock et al. Behavioral and Brain Functions 2011, 7:34 Page 6 of 7 http://www.behavioralandbrainfunctions.com/content/7/1/34 4. Nassi JJ, Callaway EM: Parallel processing strategies of the primate visual likely role of the dorsal stream in this type of non- system. Nat Rev Neurosci 2009, 10:360-372. manipulable object processing is likely to be in initiating 5. 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