Dissociation between the Perceptual and Saccadic Localization of Moving Objects

Abstract

Visual processing in the human brain provides the data both for perception and for guiding motor actions. It seems natural that our actions would be directed toward perceived locations of their targets, but it has been proposed that action and perception rely on different visual information [1-4], and this provocative claim has triggered a long-lasting debate [5-7]. Here, in support of this claim, we report a large, robust dissociation between perception and action. We take advantage of a perceptual illusion in which visual motion signals presented within the boundaries of a peripheral moving object can make the object's apparent trajectory deviate by 45° or more from its physical trajectory [8-10], a shift several times larger than the typical discrimination threshold for motion direction [11]. Despite the large perceptual distortion, we found that saccadic eye movements directed to these moving objects clearly targeted locations along their physical rather than apparent trajectories. We show that the perceived trajectory is based on the accumulation of position error determined by prior sensory history-an accumulation of error that is not found for the action toward the same target. We suggest that visual processing for perception and action might diverge in how past information is combined with new visual input, with action relying only on immediate information to track a target, whereas perception builds on previous estimates to construct a conscious representation.

Variations in crowding, saccadic precision, and spatial localization reveal the shared topology of spatial vision

“…Finally, the correlation between saccades and crowding was the weakest of all of the intertask correlations, dropping out of the hierarchical analysis when gap resolution and bisection were included as copredictors. This dissociation between crowding and saccades is consistent with the more general dissociation between perceptual and saccadic localization observed previously (40)(41)(42)(43). Note, however, that where previous studies have used trial-by-trial dissociations in speed perception and smooth pursuit to argue for distinct noise sources within a common processing stage (41, 42), we argue based on the further dissociations above that distinct spatial representations are more likely, at least for processes of spatial localization.…”

“…Recent studies suggest that there may be a particularly strong link between these processes (37)(38)(39), despite the more general dissociation between perceptual and saccadic localization (40)(41)(42)(43) and their apparently distinct cortical routes (34). Our first aim was therefore to examine whether saccadic precision and crowding covary across the visual field by measuring the size of crowded interference zones and the precision of saccade landing positions ("saccade error zones") for the same stimuli in a range of visual-field locations.…”

Diverted by dazzle: perceived movement direction is biased by target pattern orientation

“…Dynamic internal motion has been shown in a number of paradigms to influence direction perception, with judgements of trajectory being biased in the direction of internal motion, particularly when viewing targets moving in the peripheral visual field [18 -21]. Explanations of these trajectory biases have previously used models that assume faulty integration of local and global motion signals, with the local motion biasing the judgement of global motion via a vector sum mechanism [19][20][21]. Recent approaches have used a Bayesian approach to model this integration process, assuming that the visual system makes a 'best guess' at partitioning the motion signals into local and global signals, which can be biased in the case of high sensory noise, such as in peripheral viewing [46].…”

“…All stimuli travelled at 128 s 21 , and the visible trajectory length varied from approximately 11.48 to 25.98. Twelve observers took part in the experiment (10 naive and two experimenters) and each completed 288 experimental trials, divided into four equal blocks.…”

“…However, recent work has shown that these two factors can indeed interact. The perceived overall direction of a target can be strongly biased when the internal striped pattern within a moving stimulus is also moving [18][19][20][21], particularly when targets are viewed in the visual periphery, in an effect known as the motion-induced position shift [22,23]. Interestingly, some animals (such as cuttlefish) can produce similar dynamic patterns when in motion, and it has been proposed that these may have a functional role in trajectory confusion [24 -26].…”