Abstract
In the present study, the Poggendorff illusion was tested with four types of stimuli: A moving dot, a moving bar parallel to the inducing lines, a moving bar collinear to the motion trajectory, and static bars as in the classic illusion. Psychometric functions of the alignment task showed that the collinear bar, where orientation and motion trajectory matched, yielded the best alignment performance almost eliminating the illusion; the vertical bar, on the contrary, showed the worst alignment, finally the dot and the static bars led to intermediate alignments. These results demonstrate the interaction between orientation and motion trajectory that likely takes place in the primary visual cortex (V1) where these two signals might be modulated by top-down activity from higher order areas such as the middle temporal (MT). This vigorous orientation-motion trajectory interaction allows extremely accurate positional predictions of moving objects in the visual scene, in particular during occlusion.
Highlights
Natural as well as manufactured objects do trace a path behind them while they move along a trajectory in space, e.g., a dolphin swimming in the sea, an aircraft at the cruising altitude or a rocket taking-off from the ground
The collinearity of the motion trajectory with the longitudinal axis of the moving object is reminiscent, in stationary condition, of a facilitatory effect, called “contextual effect” observed in orientation selective neurons in superficial layers of V1 connected via a plexus of long-range horizontal connections (LRHC), whereby the contrast threshold for target detection is lower with nearby stimuli collinearly aligned to the target with respect to stimuli orthogonal to the target or offset with respect to the collinear path (Gilbert, Das, Ito, Kapadia, & Westheimer, 1996)
2 Results A psychometric function was generated onto the percentage of the “above” response, with respect to the total of trials for each offset of the right segment of the motion trajectory or of the motionless right bar in the four stimulus type conditions: Vertical Bar, Dot, Collinear Bar, and Static (Figure 1)
Summary
Natural as well as manufactured objects do trace a path behind them while they move along a trajectory in space, e.g., a dolphin swimming in the sea, an aircraft at the cruising altitude or a rocket taking-off from the ground. The collinearity of the motion trajectory with the longitudinal axis of the moving object is reminiscent, in stationary condition, of a facilitatory effect, called “contextual effect” observed in orientation selective neurons in superficial layers of V1 connected via a plexus of long-range horizontal connections (LRHC), whereby the contrast threshold for target detection is lower with nearby stimuli collinearly aligned to the target with respect to stimuli orthogonal to the target or offset with respect to the collinear path (Gilbert, Das, Ito, Kapadia, & Westheimer, 1996). Recent experimental evidence in primate V1, combined with psychophysical testing in human observers, suggests that the “contextual effect” might result, at least in part, from the collinear elongation of the V1 population responses in the retinotopic orientation representation (Michel, Chen, Geisler, & Seidemann, 2013)
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