83 research outputs found
Perceptual judgment and saccadic behavior in a spatial distortion with briefly presented stimuli.
When observers are asked to localize the peripheral position of a small probe
with respect to the mid-position of a spatially extended comparison stimulus,
they tend to judge the probe as being more peripheral than the mid-position of
the comparison stimulus. This relative mislocalization seems to emerge from
differences in absolute localization, that is the comparison stimulus is
localized more towards the fovea than the probe. The present study compared
saccadic behaviour and relative localization judgements in three experiments and
determined the quantitative relationship between both measures. The results
showed corresponding effects in localization errors and saccadic behaviour.
Moreover, it was possible to estimate the amount of the relative mislocalization
by means of the saccadic amplitude
Segregation of object and background motion in the retina
An important task in vision is to detect objects moving within a stationary scene. During normal viewing this is complicated by the presence of eye movements that continually scan the image across the retina, even during fixation. To detect moving objects, the brain must distinguish local motion within the scene from the global retinal image drift due to fixational eye movements. We have found that this process begins in the retina: a subset of retinal ganglion cells responds to motion in the receptive field centre, but only if the wider surround moves with a different trajectory. This selectivity for differential motion is independent of direction, and can be explained by a model of retinal circuitry that invokes pooling over nonlinear interneurons. The suppression by global image motion is probably mediated by polyaxonal, wide-field amacrine cells with transient responses. We show how a population of ganglion cells selective for differential motion can rapidly flag moving objects, and even segregate multiple moving objects
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