Category: Visual Illusions

“The brain’s ability to handle sensory information is influenced by both selective attention and consciousness. there is no consensus on the exact relationship between these two processes and whether they are distinct. so far, no experiment has simultaneously manipulated both. we carried out a full factorial 2 x 2 study of the simultaneous influences of attention and consciousness (as assayed by visibility) on perception, correcting for possible concurrent changes in attention and consciousness. we investigated the duration of afterimages for all four combinations of high versus low attention and visible versus invisible. we show that selective attention and visual consciousness have opposite effects: paying attention to the grating decreases the duration of its afterimage, whereas consciously seeing the grating increases the afterimage duration. these findings provide clear evidence for distinctive influences of selective attention and consciousness on visual perception.”

“The effect of voluntary attention on afterimage fragmentation was explored in two experiments. the afterimage, in the form of a 30 degrees-tilted star of david, was generated after prolonged steady fixation in the first experiment, and with a brief and intense flash in the second experiment. subjects were instructed to select various target shapes in the afterimage for attention and, at the same time, observe what was visible or invisible. verbal reports and manual responses to afterimage changes were analyzed. attended shapes were found to disappear from awareness faster than unattended ones (experiment 1), and complementary shapes were found to predominate visual awareness when one of the pair was selected for attention (experiment 2). voluntary attention was also found to affect closure (filling-in of enclosed regions) and smoothing of line figures in afterimages.”

“© 2015 arvo. the question of whether eye movements influence afterimage perception has been asked since the 18th century, and yet there is surprisingly little consensus on how robust these effects are and why they occur. the number of historical theories aiming to explain the effects are more numerous than clear experimental demonstrations of such effects. we provide a clearer characterization of when eye movements and blinks do or do not affect afterimages with the aim to distinguish between historical theories and integrate them with a modern understanding of perception. we found neither saccades nor pursuit reduced strong afterimage duration, and blinks actually increased afterimage duration when tested in the light. however, for weak afterimages, we found saccades reduced duration, and blinks and pursuit eye movements did not. one interpretation of these results is that saccades diminish afterimage perception because they cause the afterimage to move unlike a real object. furthermore, because saccades affect weak afterimages but not strong ones, we suggest that their effect is modulated by the ambiguity of the afterimage signal.”

“© 2015, © the author(s) 2015. the afterimage illusion refers to a complementary colored image continuing to appear in the observer’s vision after the exposure to the original image has ceased. it is assumed to be a phenomenon of the primary visual pathway, caused by overstimulation of photoreceptors of the retina. the aim of the present study was to investigate the nature of afterimage perceptions; mainly whether it is a mere physical, that is, low-level effect or whether it can be modulated by top-down processes, that is, high-level processes. participants were first exposed to five either strongly female or male faces (experiment 1), objects highly associated with female or male gender (experiment 2) or female versus male names (experiment 3), followed by a negativated image of a gender-neutral face which had to be fixated for 20 s to elicit an afterimage. participants had to rate their afterimages according to sexual dimorphism, showing that the afterimage of the gender-neutral face was perceived as significantly more female in the female priming condition compared with the male priming condition, independently of the priming quality (faces, objects, and names). our results documented, in addition to previously presumed bottom-up mechanisms, a prominent influence of top-down processing on the perception of afterimages via priming mechanisms (female primes led to more female afterimage perception).”

“We explore attentional effects on afterimages in the framework of the facade model of visual perception. we first show that the facade model can account for the experimental findings of suzuki and grabowecky [suzuki, s., & grabowecky, m. (2003). attention during adaptation weakens negative afterimages. journal of experimental psychology: human perception and performance 29, 793-807] that afterimages are weaker when the inducing stimulus is attended. we then analyze the model’s behavior with attentional influences on a two-stimulus afterimage studied by francis and rothmayer [francis, g., & rothmayer, m. (2003). interactions of afterimages for orientation and color: experimental data and model simulations. perception & psychophysics 65, 508-522]. the model predicts that attentional focus directed towards the first stimulus has little effect on afterimage strength. in contrast, the model predicts that attentional focus on the second stimulus should increase the strength of the afterimage compared to when attention is focused elsewhere. moreover, the model predicts that the attentional effects on the second stimulus should vary with time after offset of the second inducing stimulus. all of the model predictions are validated in an experiment. the model and experimental results extend and clarify previous explanations of attentional effects and afterimages. © 2007 elsevier ltd. all rights reserved.”

“Of what it signifies, any photographic image also connotes memory and nostalgia, nostalgia formodernity and the twentieth century, the era of the pre-digital, pre-’ postmodern. regardless ofwhat it represents, any photographic image today first of all represents photography. …”

“Retinal ganglion cells convey the visual image from the eye to the brain. they generally encode local differences in space and changes in time rather than the raw image intensity. this can be seen as a strategy of predictive coding, adapted through evolution to the average image statistics of the natural environment. yet animals encounter many environments with visual statistics different from the average scene. here we show that when this happens, the retina adjusts its processing dynamically. the spatio-temporal receptive fields of retinal ganglion cells change after a few seconds in a new environment. the changes are adaptive, in that the new receptive field improves predictive coding under the new image statistics. we show that a network model with plastic synapses can account for the large variety of observed adaptations.”