Abstract
One of the most important tasks for the visual system is to construct an internal representation of the spatial properties of objects, including their size. Size perception includes a combination of bottom-up (retinal inputs) and top-down (e.g., expectations) information, which makes the estimates of object size malleable and susceptible to numerous contextual cues. For example, it has been shown that size perception is prone to adaptation: brief previous presentations of larger or smaller adapting stimuli at the same region of space changes the perceived size of a subsequent test stimulus. Large adapting stimuli cause the test to appear smaller than its veridical size and vice versa. Here, we investigated whether size adaptation is susceptible to attentional modulation. First, we measured the magnitude of adaptation aftereffects for a size discrimination task. Then, we compared these aftereffects (on average 15–20%) with those measured while participants were engaged, during the adaptation phase, in one of the two highly demanding central visual tasks: Multiple Object Tracking (MOT) or Rapid Serial Visual Presentation (RSVP). Our results indicate that deploying visual attention away from the adapters did not significantly affect the distortions of perceived size induced by adaptation, with accuracy and precision in the discrimination task being almost identical in all experimental conditions. Taken together, these results suggest that visual attention does not play a key role in size adaptation, in line with the idea that this phenomenon can be accounted for by local gain control mechanisms within area V1.
Highlights
Achieving a reliable representation of the surrounding space is one of the most critical tasks that the animals’ brain has to accomplish
Even in this case, the magnitude of size adaptation indicated by the averaged PSEs achieved when participants were engaged with the central task (y axis position of cyan star in Figure 3A, mean 5.74, SD = 0.46) was found to be similar to the condition in which no central task was performed (x axis of the cyan star in Figure 3A, mean 5.77, SD = 0.2). This adaptation magnitude turned out to be similar to those achieved in Exp. 1 when no central stimuli were displayed at all [a oneway ANOVA: F(2,16) = 2.3, p = 0.31, ges = 0.137]. Taken together these results suggest that neither the increase of sensory load induced by the mere presentation of the central stimuli, nor the shift of attentional resources away from the adapters significantly affect the magnitude of size adaptation aftereffects
We investigated the role of attention in mediating size adaptation aftereffects, i.e., distortions of perceived size of visual objects induced by the relative size of stimuli previously displayed in the same area of the visual field
Summary
Achieving a reliable representation of the surrounding space is one of the most critical tasks that the animals’ brain (including humans) has to accomplish. Accurate judgment of the size or distance of the objects in the environment is critical for survival as it allows to successfully interact with them. Much research has been dedicated to unveil the brain mechanisms underpinning objects’ size perception. The exact mechanisms that underlie size perception are yet poorly understood (Schwarzkopf et al, 2010). One important characteristic of size perception demonstrated by many studies is its susceptibility to contextual effects. In the Ebbinghaus illusion (Massaro and Anderson, 1971), two identical circles surrounded by large and small stimuli are perceived as having
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