hide
Free keywords:
-
Abstract:
Actions often occur in the visual periphery. Here we measured the spatial extent of action sensitive perceptual channels across the visual field using a behavioral action adaptation paradigm. Participants viewed an action (punch or handshake) for a prolonged amount of time (adaptor) and subsequently categorized an ambiguous test action as either 'punch' or 'handshake'. The adaptation effect refers to the biased perception of the test stimulus due to the prolonged viewing of the adaptor and the resulting loss of sensitivity to that stimulus. Therefore the more a channel responds to a specific stimulus the higher is the adaptation effect for that certain channel. We measured the size of the adaptation effect as a function of the spatial distance between adaptor and test stimuli in order to determine if actions can be processed in spatially distinct channels. Specifically, we adapted participants at 0° (fixation), 20° and 40° eccentricity in three separate conditions to measure the putative spatial extent of action channels at these positions. In each condition, we measured the size of the adaptation effect at -60°,-40°,-20°, 0°,20°,40°,60° of eccentricity. We fitted Gaussian functions to describe the channel response of each condition and used the full width at half maximum (FWHM) of the Gaussians as a measure of the spatial extent of the action channels. In contrast to previous reports of an increase of midget ganglion cell dendritic field size with eccentricity (Dacey, 1993), our results showed that FWHM decreased with eccentricity (FWHM at 0°: 56°, FWHM at 20°: 29, FWHM at 40°: 26). We then asked whether the response of these action sensitive perceptual channels can be used to predict average recognition performance (d') of social actions across the visual field obtained in a previous study (Fademrecht et al. 2014). We used G(x) - the summed response of all three channels at eccentricity x, to predict recognition performance at eccentricity x. A simple linear transformation of the summed channel response of the form a+b*G(x) was able to predict 95.5 of the variation in the recognition performance. Taken together these results demonstrate that actions can be processed in separate spatially distinct perceptual channels, their FWHM decreases with eccentricity and can be used to predict action recognition performance in the visual periphery.
