Spatial mislocalization as a consequence of sequential coding of stimuli

Abstract

In three experiments, we tested whether sequentially coding two visual stimuli can create a spatial misperception of a visual moving stimulus. In Experiment 1, we showed that a spatial misperception, the flash-lag effect, is accompanied by a similar temporal misperception of first perceiving the flash and only then a change of the moving stimulus, when in fact the two events were exactly simultaneous. In Experiment 2, we demonstrated that when the spatial misperception of a flash-lag effect is absent, the temporal misperception is also absent. In Experiment 3, we extended these findings and showed that if the stimulus conditions require coding first a flash and subsequently a nearby moving stimulus, a spatial flash-lag effect is found, with the position of the moving stimulus being misperceived as shifted in the direction of its motion, whereas this spatial misperception is reversed so that the moving stimulus is misperceived as shifted in a direction opposite to its motion when the conditions require coding first the moving stimulus and then the flash. Together, the results demonstrate that sequential coding of two stimuli can lead to a spatial misperception whose direction can be predicted from the order of coding the moving object versus the flash. We propose an attentional sequential-coding explanation for the flash-lag effect and discuss its explanatory power with respect to related illusions (e.g., the Fröhlich effect) and other explanations.

Right away: A late, right-lateralized category effect complements an early, left-lateralized category effect in visual search

“…With this, the left-lateralized category effect is similar to other short-lived attentional processes that can bias visual selection to particular items. Such attentional biases can also alter our perception of these stimuli, as attention can reliably accelerate the perceived timing of events (Hikosaka, Miyauchi, & Shimojo, 1999;Priess, Scharlau, Becker, & Ansorge, 2012) and increase the perceived contrast and resolution of the attended stimulus (Carrasco, Ling, & Read, 2004;Yeshurun & Carrasco, 1998). Given these findings, it is plausible that acrosscategory targets are perceived differently in the right versus the left hemifield, whereas it still remains to be shown whether p < .01, as per two-tailed t tests facilitated visual selection of across-category target in the RVF is indeed due to the involvement of language (e.g., due to the proximity of corresponding brain areas), or to a different, language-independent hemispheric specialization.…”

Does attention speed up processing? Decreases and increases of processing rates in visual prior entry

“…Most likely, there would only be the purely facilitatory prior-entry component as there is no distractor to initiate a bounce. By contrast, for prior entry in the flash-lag paradigm (a mismatch between the perceived location of a moving and a briefly exposed stimulus), as investigated by Priess, Scharlau, Becker, and Ansorge (2012), acceleration as well as deceleration can contribute. It can either be that processing of the flash, which is assumed to attract attention, is accelerated or that processing the moving stimulus is slowed down.…”