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Debbie Giaschi
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Motion Perception
UBC Vision Lab
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Visual Neuroscience Lab

Motion Research

Select Abstracts from Completed Projects

Meier, K., & Giaschi, E. (2017). Effect of spatial and temporal stimulus parameters on the maturation of global motion perception.Vision Research 135, 1-9.

There are discrepancies with respect to the age at which adult-like performance is reached on tasks assessing global motion perception. This is in part because performance in children depends on stimulus parameters. We recently showed that five-year-olds demonstrated adult-like performance over a range of speeds when the speed ratio was comprised of longer spatial and temporal displacements; but displayed immature performance whenthe speed ratio was comprised of shorter displacements. The goal of the current study was to assess the effect of these global motion stimulus parameters across a broader age range in order to estimate the age at which mature performance is reached. Motion coherence thresholds were assessed in 182 children and adults aged 730 years. Dot displacement (Dx) was 1, 5, or 30 min of arc; frame duration (Dt) was 17 or 50 ms. This created a total of six conditions. Consistent with our previous results, coherence thresholds in the youngest children assessed were adult-like at the two conditions with the largest Dx. Maturity was reached around age 12 for the medium Dx, and by age 16 for the smallest Dx. Performance did not appear to be affected by Dt. This late maturation may reflect a long developmental period for cortical networks underlying global motion perception. These findings resolve many of the discrepancies across previous studies, and should be considered when using global motion tasks to assess children with atypical development.

Meier, K., & Giaschi, E. (2014). The maturation of global motion perception depends on the spatial and temporal offsets of the stimulus.Vision Research 91, 61-67.

The typical development of motion perception is commonly assessed with tests of global motion integration using random dot kinematograms. There are discrepancies, however, with respect to when typically- developing children reach adult-like performance on this task, ranging from as early as 3 years to as late as 12 years. To address these discrepancies, the current study measured the effect of frame duration (t) and signal dot spatial offset (x) on motion coherence thresholds in adults and children. Two t values were used in combination with seven x values, for a range of speeds (0.338 deg/s). Developmental comparisons showed that for the longer t, children performed as well as adults for larger x, and were immature for smaller x. When parameters were expressed as speed, there was a range of intermediate speeds (412 deg/s) for which maturity was dependent on the values of x and t tested. These results resolve previous discrepancies by showing that motion sensitivity to a given speed may be mature, or not, depending on the underlying spatial and temporal properties of the motion stimulus.

Narasimhan, S & Giaschi, D (2012). The effect of dot speed and density on the development of global motion perception. Vision Research 62,102-107.

The purpose of this study was to investigate the effect of dot speed and dot density on the development of global motion perception by comparing the performance of adults and children (56 years old) on a direction-discrimination task. Motion coherence thresholds were measured at two dot speeds (1 and 4 deg/s) and three dot densities (1, 15, 30 dots/deg2). Adult coherence thresholds were constant at approximately 9%, regardless of speed or density. Child coherence thresholds were significantly higher across conditions, and were most immature at the slow speed and at the sparse density. Thus, the development of global motion perception depends heavily on stimulus parameters. This finding can account for some of the discrepancy in the current developmental literature. Our results, however, caution against making general claims about motion deficits in clinical populations based on only a single measurement at a specific combination of speed and density.

Hayward J, Truong G, Partanen M, Giaschi D. (2011) Effects of speed, age, and amblyopia on the perception of motion-defined form Vision Research 51 (20), 2216-2223.

We determined the effect of dot speed on the typical and atypical development of motion-defined form perception. Monocular motion coherence thresholds for orientation discrimination of motion-defined rectangles were determined at slow (0.1 deg/s), medium (0.9 deg/s) and fast (5.0 deg/s) dot speeds. First we examined typical development from age 4 to 31 years. We found that performance was most immature at the slow speed and in the youngest group of children (46 years). Next we measured motion-defined form perception in the amblyopic and fellow eyes of patients with amblyopia. Deficits were found in both eyes and were most pronounced at the slow speed. These results demonstrate the importance of dot speed to the development of motion-defined form perception. Implications regarding sensitive periods and the neural correlates of motion-defined form perception are discussed.

Zwicker A, Hoag R, Edwards V, Boden C, Giaschi D (2006) The effects of optical blur on motion and texture perception. Optometry and Vision Science 83, 382-390.

Purpose. The purpose of this study is to determine how decreased visual acuity affects performance on tasks of motion and texture perception. Methods. Positive diopter lenses were used to match three subjects at five levels of decimal visual acuity (DVA) ranging from an uncorrected DVA of 1.6 to the lowest DVA of 0.2. Performance thresholds were determined at each acuity level for five different psychophysical tasks. The tasks assessed the perception of motion-defined form, global motion, maximum motion displacement (Dmax), texture-defined form, and global texture. Results. Reducing visual acuity decreased performance on the tasks of motion-defined form identification, texture-defined form identification, and global texture integration. Performance on the Dmax task improved with a reduction in visual acuity. Performance on the global motion task was unaffected by changes in visual acuity. Conclusions. Visual acuity should be considered when interpreting the results of developmental or clinical studies of motion and texture perception. The only exception to this is global motion perception, at least when DVA is better than 0.2. The effect of blur on tasks of motion and texture perception may reflect the extent to which high spatial frequency information is required for performance on these tasks.

Zwicker A, Giaschi D (2005) Speed-tuned global motion mechanisms. Journal of Vision, 5(8):840a.

Asymmetries in global motion perception have been noted for many directions of motion; yet, consistent directional asymmetries have not emerged. At VSS 2004 we reported preliminary direction discrimination results based on a slow speed of motion. We now extend those findings to a faster speed of motion. We investigated the effect of direction, speed and visual field location on global motion processing in 40 university students using random dot kinematograms. Coherence thresholds for direction discrimination using a 2 AFC paradigm were obtained for horizontal (left or right) and vertical motion (up or down), at slow (1 deg/s) and fast (8 deg/s) speeds in the full-field, and four hemifields (left, right, top, bottom). At the fast speed, horizontal coherence thresholds were lower than vertical thresholds, an effect found previously (e.g. Raymond, 1994). This effect was qualified by an interaction with location such that horizontal thresholds were significantly lower than vertical thresholds when motion was presented in the full-field and the top and bottom hemifields, but not when motion was in just the right or left hemifields. Conversely, there was no difference between horizontal and vertical thresholds and no effect of visual field location when the speed of motion was slow. Further, there was a trend for coherence thresholds to be lower for faster motion than for slower motion. Taken together, these results suggest that there are different mechanisms involved in processing slow and fast global motion, and that direction discrimination may be dependent upon speed-tuned mechanisms. This is consistent with past global motion research in which fast-moving noise dots did not impair extraction of motion signals carried by slow-moving dots (Edwards et al., 1998). Edwards and his colleagues suggested that global motion extraction occurs within speed-tuned systems; our results suggest differences in direction discrimination within these speed-tuned systems.

Chapman C, Hoag R, Giaschi D (2004) The effect of disrupting the human magnocellular pathway on global motion perception Vision Research 44, 2551-2557.

The purpose of this study was to demonstrate the effect of human magnocellular (M)-pathway disruption on global motion perception. Coherence thresholds for global motion direction discrimination in random dot patterns were determined at slow and moderate dot speeds: (1) after adaptation to full-field sinusoidal flicker or a steady gray field, and (2) on a red or a gray background. Adaptation to flicker and a red background increased motion coherence thresholds relative to the gray baseline conditions at both dot speeds. Physiological studies have shown that M cells in the retina and LGN are inhibited by red light and are a main contributor to flicker perception in monkeys. Therefore, our results suggest that interference with processing in the subcortical M pathway disrupts higher-level motion integration.

Giaschi D (2006) The processing of motion-defined form. In: Harris L and Jenkin M(eds) Seeing Spatial Form. Oxford University Press, New York, pp. 101-119.

Motion contrast is just one way to define edges that yield figure-ground segregation. Regan, Giaschi and colleagues studied motion-defined (MD) form perception in several different patient groups. We concluded that although MD form identification was a sensitive indicator of abnormal visual processing, it should not be considered an indicator of abnormal magnocellular function. We also suggested that interconnections between the dorsal motion pathway and the ventral form pathway were important for MD form perception. Surprisingly, our work has been cited as evidence that performance on MD form tasks reflects the functioning of the magnocellular/dorsal stream. My current work uses psychophysical studies with children and functional MRI to further refute this interpretation by comparing MD form with global motion and texture-defined (TD) form perception. Global motion perception is mature by age 3, is not affected by optical blur, is abnormal in children with dyslexia and is normal in children with amblyopia. MD form perception continues to mature until age 6, becomes impossible in the presence of blur, is normal in dyslexia and is abnormal in amblyopia. TD form perception is similar to MD form perception with respect to age of maturation and effect of blur. Global motion activates cortical area V5/MT and other motion-sensitive posterior visual areas. MD and TD form activate cortical areas LOC and IT, but not V5/MT when the appropriate baseline condition is used. These results suggest that the processing of MD form is more similar to the processing of TD form (both involve figure-ground segregation) than to the processing of global motion (both involve spatial integration of local motion signals).

Tata M, Giaschi D (2004) Warning: Attending to a mask may be hazardous to your perception. Psychonomic Bulletin & Review, 11, 262-268.

Object substitution is a type of backward masking that occurs when a mask appears during visual search for a target. We tested the hypothesis that object substitution is an overwriting process triggered by attentional selection of the mask. Impeding attentional selection of a mask by embedding it in an array of distractors eliminated object substitution. Similarly, object substitution did not occur when the mask appeared in advance of the target and, therefore, could not capture attention during search for the target. However, masking was reinstated when the mask was revealed from background contours at the moment of target onset and could therefore capture attention during search. These observations demonstrate that attentional selection of the mask is a necessary step in this type of masking and suggest that object substitution is active overwriting of unattended information triggered by selection of other visual information at a nearby location.

Zwicker A, Giaschi D (2004) Directional anisotropies for full-field and hemifield global motion processing. Journal of Vision, 4(8), 848.

Previous research suggests that certain directions of motion are perceived more readily than others (e.g. Ohtani & Ejima, 1997; Raymond, 1994; Rottach et al., 1996). A consistent pattern of directional anisotropies however, has yet to emerge. Directional anisotropies for global motion perception were studied in 20 university students using random dot kinematograms (RDKs). Coherence thresholds were obtained for horizontal (left or right) and vertical (up or down) directions of motion for full-field, upper-hemifield, lower-hemifield, left-hemifield and right-hemifield RDKs. Consistent with past research, a trend toward lower thresholds for horizontal global motion relative to vertical motion was found. Separate analyses of upward, downward, leftward and rightward motion, however, revealed lower coherence thresholds for upward motion relative to all other directions of motion. This effect was occluded by higher thresholds for downward motion, relative to all other directions of motion, when downward and upward directions were paired. Finally, lower coherence thresholds were obtained for upper-hemifield RDKs, relative to the other hemifield conditions. Cortical areas MT/MST have been indicated as primary components of global motion processing, but the anisotropies reported here have not yet been described in monkey single-unit or human neuroimaging studies. The neural basis for directional and hemifield differences in motion processing is not currently known. Evolutionarily, it may be that these asymmetries in motion sensitivity developed to counteract disproportionate downward motion, as well as the more common occurrence of inferiorly presented motion cues in the surrounding environment.

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