Aftereffects

Neural correlates of affective judgments with visual stimuli

Kleovoulos Tsourides, Evan Ehrenberg, Christopher Simons and Pawan Sinha

Our perception of many visual stimuli is accompanied by implicit or explicit assessments of how 'likable' they are. An image of a bowl of cherries, for instance, is attractive while one of moldy bread is not. Here we report results from our electrophysiological studies that were designed to identify the neural correlates of these judgments. Our stimuli depicted food or non-food items with sub-classes of appealing or unappealing exemplars. We sought to determine whether these four classes of stimuli could be distinguished based on the patterns of brain activity they elicited, the consistency of responses across subjects, as well as the time-course of emergence of these responses.Subjects passively viewed 200 visual stimuli (50 from each class) while their brain activity was recorded using magneto-encephalography (MEG). We found compelling differences in brain activity patterns corresponding to the four stimulus classes, with the first distinction emerging as early as 85 ms post stimulus onset. The identification of these neural correlates furthers our understanding of the substrates of affective judgments and has applied implications in the domains of design and evaluation.

Influences of spatial and featural endogenous attention on pattern rivalry for afterimages

Eric A. Reavis, Peter J. Kohler, Gideon P. Caplovitz, Thalia P. Wheatley and Peter U. Tse

Perceptual multistability can result from ambiguous sensory input consistent with multiple perceptual interpretations. In such cases, including monocular rivalry, binocular rivalry, perception of ambiguous figures, and the like, visual experience tends to alternate between several perceptual interpretations of the stimuli. Understanding what mechanisms contribute to the selection of a particular interpretation for perceptual dominance during perceptual multistability may provide clues to the selection processes that influence the contents of visual perception under normal circumstances. Here, we demonstrate that endogenous attention can influence perceptual dominance for afterimages engaged in (monocular) pattern rivalry, much as exogenous cues such as contour presence can (see van Lier, Vergeer, & Anstis, 2009). Using rivalrous afterimages of overlapping, colored, transparent textures and a post-adaptation auditory attentional cue, we find that endogenous attention can lengthen the dominance period of the attended stimulus. We performed additional experiments to isolate the contributions of spatial and featural attention to the effect. The results of those experiments suggest that spatial and featural attention have dissociable effects that can combine additively. Thus, our findings suggest that different types of endogenous attention can contribute to the selection of particular perceptual interpretations in pattern rivalry for afterimages.

Dichoptic positive color after image is limited for the number of colors presented within a display

Takao Sato and Yutaka Nakajima

We have reported that negative color afterimage is enhanced when the adapted are is surrounded by a luminance contour in the test phase. In addition, positive color afterimage (PCAI) is observed when the inducer was presented to the opposite eye (ECVP, 2010). It is well known that black and white photos appear colored when viewed after adapting to a complementary color image. However, PCAI was never observed when a B/W photo was presented to the opposite eye as for dichoptic PCAI. This suggests that the occurrence of PCAE is limited by spatial complexity, or number of colors. To test these possibilities, we examined the dichoptic PCAE by varying number of divide areas and/or colors using curved Mondrian patterns. The stimulus was a 15 x 9 deg rectangle divided into either 7 or 30 sections and each sections was filled with one of either 2, 4, 12, or 30 different colors. The results indicated no effect of number of colors, but clear effects of number of areas were revealed. These results therefore indicated that dichoptic PCAE occurs only for patterns with relatively simple spatial configuration, and suggest the absence of dichoptic PCAE in photographic stimulus arises from the same limitation.

Emotional action aftereffects indicate dual emotion coding mechanisms

Joanna Wincenciak, Jennifer S. Ingham, Tjeerd Jellema and Nick E. Barraclough

Face aftereffects suggest partially independent coding of facial expressions and facial identity (Fox & Barton, 2007, Brain Research, 1127(1), 80-89). Bodily actions can also convey actor identity and emotional state. We investigated the mechanisms involved in recognising emotions from whole body actions using a visual adaptation paradigm. Following adaptation to actions performed in either a happy or sad fashion participants interpreted subsequent actions performed in a neutral fashion as portraying the opposite emotion. Emotional action aftereffects were stronger when the identity of the actor in the adapting and test stimuli was the same, than when it was different. Both identity dependent and identity independent emotional action aftereffects increased with the duration of the adapting stimuli. However, the different identity aftereffect quickly decayed over time, while the same identity aftereffect had still not decayed after 10.8 sec. These findings suggest that adapting to emotional actions influences 2 separate mechanisms. Following adaptation, an identity independent emotional action coding mechanism shows visual aftereffects with dynamics similar to other high-level aftereffects. A second identity dependent emotional action coding mechanism, however, shows different adaptation dynamics, where adaptation results in a long lasting recalibration of the perceived emotion derived from the actions of the observed individual.

Attractiveness of face photographs: Adaptation effects and spatial frequency characteristics in the Fourier domain

Gregor Hayn-Leichsenring, Christoph Redies, Nadine Kloth and Stefan Schweinberger

We studied visual adaptation on face attractiveness (defined as the physical allurement of a person). First, we found an adaptation effect on attractiveness of non-morphed photographs of human adult faces. This adaptation effect is non-symmetric, suggesting that adaptation on attractive face photographs has a larger effect than on unattractive faces. The observed effect may relate to the finding that attractive faces are more tightly clustered in psychological face space than unattractive faces [Valentine and Bruce, 1986, Perception, 15(5), 525-535]. Next, we asked whether the rating of attractiveness is correlated with image properties that have been previously associated with aesthetic visual perception, i.e. their spatial frequency spectra in the Fourier domain [Graham and Redies, 2010, Vision Research 50(16):1503-1509]. We demonstrate that Fourier power and the slope of log-log plots of radially averaged (1d) Fourier power correlates with the attractiveness ratings obtained in the previous experiment. In conclusion, the adaptation study suggests that specific neural circuits mediate the perception of face attractiveness in the human visual system. Moreover, beyond individual preferences, face attractiveness ratings are associated with measurable, higher-order statistical properties of the face images.

Does top-down information influence the afterimage illusion?

Sandra Utz and Claus-Christian Carbon

The afterimage illusion refers to a (complementary coloured) 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. According to Hering’s opponent process theory, the more fatigue of certain pathways the stronger the probability of producing antagonistic visual impression, for instance overstimulation evoked by areas of red will produce an afterimage of green. Aim of the present study was to investigate the origin of afterimage perceptions, mainly whether it is a mere physical effect or whether it can be influenced by top-down processes, e.g. by an implicit memory task. Using a priming paradigm, participants were presented with five either strongly female or male faces, followed by a negative image of an androgynous face which had to be fixated for 20s. Participants had to rate their afterimages according to sexual dimorphism. Results showed that the afterimage of the gender-neutral face was perceived as significantly more female in the female priming condition in comparison to the male priming condition (medium effect size). Our results clearly argue for a prominent influence of top-down processing on the afterimage illusion.