Motion discontinuities can signal object boundaries where few or no other cues, such as luminance, colour, or texture, are available. Hence, motion-defined contours are an ecologically important counterpart to luminance contours. We developed a novel motion-defined Gabor stimulus to investigate the nature of neural operators analysing visual motion fields in order to draw parallels with known luminance operators. Luminance-defined Gabors have been successfully used to discern the spatial-extent and spatial-frequency specificity of possible visual contour detectors. We now extend these studies into the motion domain. We define a stimulus using limited-lifetime moving dots whose velocity is described over 2-D space by a Gabor pattern surrounded by randomly moving dots. Participants were asked to determine whether the orientation of the Gabor pattern (and hence of the motion contours) was vertical or horizontal in a 2AFC task, and the proportion of correct responses was recorded. We found that with practice participants became highly proficient at this task, able in certain cases to reach 90% accuracy with only 12 limited-lifetime dots. However, for both practised and novice participants we found that the ability to detect a single boundary saturates with the size of the Gaussian envelope of the Gabor at approximately 5 deg full-width at half-height. At this optimal size we then varied spatial frequency and found the optimum was at the lowest measured spatial frequency (0.1 cycle deg-1 ) and then steadily decreased with higher spatial frequencies, suggesting that motion contour detectors may be specifically tuned to a single, isolated edge.
|Publication status||Unpublished - 2006|
|Event||11th Applied Vision Association Christmas Meeting - Aston University, Birmingham (UK), United Kingdom|
Duration: 18 Dec 2006 → …
|Other||11th Applied Vision Association Christmas Meeting|
|City||Aston University, Birmingham (UK)|
|Period||18/12/06 → …|
Bibliographical noteAbstract published in Eleventh Applied Vision Christmas Meeting, in Perception, 2007, 36(2), pp. 304-305, ISSN 0001-4966.
- motion discontinuities
- object boundaries
- motion-defined contours
- luminance contour
- visual motion fields
- luminance operators
- motion contour detectors