(Don't) look where you are going: Evidence for a travel direction signal in humans that is independent of head direction

We often assume that travel direction is redundant with head direction, but from first principles, these two factors provide differing spatial information. Although head direction has been found to be a fundamental component of human navigation, it is unclear how self-motion signals for travel direction contribute to forming a travel trajectory. Employing a novel motion adaptation paradigm from visual neuroscience designed to preclude a contribution of head direction, we found high-level aftereffects of perceived travel direction, indicating that travel direction is a fundamental component of human navigation. Interestingly, we discovered a higher frequency of reporting perceived travel toward the adapted direction compared to a no-adapt control-an aftereffect that runs contrary to low-level motion aftereffects. This travel aftereffect was maintained after controlling for possible response biases and approaching effects, and it scaled with adaptation duration. These findings demonstrate the first evidence of how a pure travel direction signal might be represented in humans, independent of head direction. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Frequency of adapting events affects face aftereffects but not blur aftereffects

The dynamics of visual adaptation remain poorly understood. Recent studies have found that the strength of adaptation aftereffects in the perception of numerosity depends more strongly on the number of adaptation events than on the duration of the adaptation. We investigated whether such effects can be observed for other visual attributes. We measured blur (perceived focus-sharp vs blurred adapt) and face (perceived race- Asian vs. White adapt) aftereffects by varying the number of adaptation events (4 or 16) and the duration of each adaptation event (0.25 s or 1 s). We found evidence for an effect of event number on face but not on blur adaptation, though the effect for faces was significant for only one of the two face adapt conditions (Asian). Our results suggest that different perceptual dimensions may vary in how adaptation effects accrue, potentially because of differences in factors such as the sites (early or late) of the sensitivity changes or nature of the stimulus. These differences may impact how and how rapidly the visual system can adjust to different visual properties.

Tilt aftereffect spreads across the visual field

The tilt aftereffect (TAE) is observed when adaptation to a tilted contour alters the perceived tilt of a subsequently presented contour. Thus far, TAE has been treated as a local aftereffect observed only at the location of the adapter. Whether and how TAE spreads to other locations in the visual field has not been systematically studied. Here, we sought an answer to this question by measuring TAE magnitudes at locations including but not limited to the adapter location. The adapter was a tilted grating presented at the same peripheral location throughout an experimental session. In a single trial, participants indicated the perceived tilt of a test grating presented after the adapter at one of fifteen locations in the same visual hemifield as the adapter. We found non-zero TAE magnitudes in all locations tested, showing that the effect spreads across the tested visual hemifield. Next, to establish a link between neuronal activity and behavioral results and to predict the possible neuronal origins of the spread, we built a computational model based on known characteristics of the visual cortex. The simulation results showed that the model could successfully capture the pattern of the behavioral results. Furthermore, the pattern of the optimized receptive field sizes suggests that mid-level visual areas, such as V4, could be critically involved in TAE and its spread across the visual field.

Experience-dependent reshaping of body gender perception

Protracted exposure to specific stimuli causes biased visual aftereffects at both low- and high-level dimensions of a stimulus. Recently, it has been proposed that alterations of these aftereffects could play a role in body misperceptions. However, since previous studies have mainly addressed manipulations of body size, the relative contribution of low-level retinotopic and/or high-level object-based mechanisms is yet to be understood. In three experiments, we investigated visual aftereffects for body-gender perception, testing for the tuning of visual aftereffects across different characters and orientation. We found that exposure to a distinctively female (or male) body makes androgynous bodies appear as more masculine (or feminine) and that these aftereffects were not specific for the individual characteristics of the adapting body (Exp.1). Furthermore, exposure to only upright bodies (Exp.2) biased the perception of upright, but not of inverted bodies, while exposure to both upright and inverted bodies (Exp.3) biased perception for both. Finally, participants' sensitivity to body aftereffects was lower in individuals with greater communication deficits and deeper internalization of a male gender role. Overall, our data reveals the orientation-, but not identity-tuning of body-gender aftereffects and points to the association between alterations of the malleability of body gender perception and social deficits.

The McCollough World: Induction of orientation-contingent aftereffects with an altered-reality system

The McCollough Effect is a color aftereffect produced by exposure to colored, oriented patterns. For example, following adaptation to vertical red and horizontal green stripes in alternation, vertical black and white patterns appear greenish, while horizontal black and white patterns appear reddish. The striking aspect of the McCollough Effect is that just a few minutes of adaptation can produce an aftereffect lasting days or weeks. Though this effect is easily induced, previous work has shown that stronger effects can be achieved with longer periods of adaptation. To allow especially long adaptation durations, the current work develops a novel method of induction of the McCollough Effect using live video feed, filtered by orientation, and viewed with a head-mounted display. Results showed that this "McCollough World" paradigm was as strong an inducer (per unit time) as traditional paradigms using gratings, while allowing observers to adapt comfortably for multiple hours. Two hours of McCollough World adaptation produced effects that were significantly larger than 20 min of traditional adaptation, which is close to the tolerance limits for gratings. This work provides insight into the features necessary for induction of the McCollough Effect and provides a strategy for creating especially strong and long-lasting color aftereffects.

Cross-modal motion aftereffects transfer between vision and touch in early deaf adults

Previous research on early deafness has primarily focused on the behavioral and neural changes in the intact visual and tactile modalities. However, how early deafness changes the interplay of these two modalities is not well understood. In the current study, we investigated the effect of auditory deprivation on visuo-tactile interaction by measuring the cross-modal motion aftereffect. Consistent with previous findings, motion aftereffect transferred between vision and touch in a bidirectional manner in hearing participants. However, for deaf participants, the cross-modal transfer occurred only in the tactile-to-visual direction but not in the visual-to-tactile direction. This unidirectional cross-modal motion aftereffect found in the deaf participants could not be explained by unisensory motion aftereffect or discrimination threshold. The results suggest a reduced visual influence on tactile motion perception in early deaf individuals.

Hemisphere-specific properties of the ventriloquism aftereffect

Visual calibration of auditory space requires re-alignment of representations differing in (1) format (auditory hemispheric channels vs visual maps) and (2) reference frames (head-centered vs eye-centered). Here, a ventriloquism paradigm from Kopčo, Lin, Shinn-Cunningham, and Groh [J. Neurosci. 29, 13809-13814 (2009)] was used to examine these processes in humans for ventriloquism induced within one spatial hemifield. Results show that (1) the auditory representation can be adapted even by aligned audio-visual stimuli, and (2) the spatial reference frame is primarily head-centered, with a weak eye-centered modulation. These results support the view that the ventriloquism aftereffect is driven by multiple spatially non-uniform, hemisphere-specific processes.

[Research advances on the duration aftereffect]

Recent sensory history plays a critical role in the perception of event duration. For example, repetitive exposure to a particular duration leads to the distortion of subsequent duration perception. This phenomenon, termed duration adaptation, induces a robust repulsive duration aftereffect. In particular, adaptation to relatively long sensory events shortens the perceived duration of a subsequent event, while adaptation to relatively short sensory events lengthens the perception of subsequent event durations. This phenomenon implies the plasticity of duration perception and offers important clues for revealing the cognitive neural mechanism of duration perception. Duration aftereffect has received more and more attention in recent years. In this review, we introduce recent research advances in our understanding of duration aftereffect, especially with regards to its manifestations, origin, and cognitive neural mechanisms. We also propose possible directions for future research. In sum, we posit that studies on the duration aftereffect phenomenon are helpful in understanding general duration perception, and as such, should receive more attention in future.

Contrast and Stimulus Intensity in Kinesthetic Figural Aftereffects with Normal and Schizophrenic Subjects

A proprioceptive size estimation task was used to assess the magnitude of kinesthetic figural aftereffects between schizophrenics and normals. College students (controls) demonstrated the largest kinesthetic figural aftereffects. Acute schizophrenics showed less responsivity than normals to proprioceptive stimulation and chronic schizophrenics manifested the lowest mean kinesthetic figural aftereffects score of the three groups. The results were discussed as evidence in support of the hypothesis of a proprioceptive deficit in schizophrenia. The results also were interpreted as casting some doubt on the validity of the concept of kinesthetic control of stimulus intensity in schizophrenic size-estimation performance.

Counter Displacement in the Visual Figural After-effect

In this study an attempt is made to specify the conditions under which counter displacement (test contour displaced toward the inspection contour) will occur. Three experiments are described in which different lengths of inspection of the test-(T-) figure are given following short and long inspections of the inspection-(I-) figure. In Experiment I, after partial dissipation of the figural after-effect (FAE), a period of continuous inspection of the T-figure was employed. In Experiments II and III distributed inspection of the T-figure was given by increasing the number of measurements of the FAE. In all experiments counter displacement was evident. The results were consistent with an interpretation of counter displacement offered earlier by the authors.

Adaptation and Repulsion in the Figural After-effect

An experiment is reported which shows the effect of inspection of a curved line on the apparent curvature of a curved test line for a range of curvatures of both I and T lines. A second experiment extends the range of I curvatures, using only one T line, a straight line. The experiments showed both adaptation and repulsion components in the FAE.

An experiment by Kohler and Wallach which could not be reconciled with these results was repeated in the relevant part; the results were in agreement with the first experiment here and did not agree with those obtained by Kohler and Wallach.

An argument is presented that both adaptation and repulsion effects could be produced by a cell adaptation mechanism.

Pulling Faces: An Investigation of the Face-Distortion Aftereffect

After adaptation to a face distorted to look unnaturally thin or fat, a normal face appears distorted in the opposite direction (Webster and MacLin 1999 Psychonomic Bulletin & Review6 647–653). When the adapting face is oriented 45° from vertically upright and the test face 45° in the opposite direction, the axis of perceived distortion changes with the orientation of the face. The magnitude of this aftereffect shows a reduction of approximately 40% from that found when both adapting and test faces are tilted identically. This finding suggests that to a large degree the aftereffect is mediated not by low-level retinotopic (image-based) visual mechanisms but at a higher level of object-based processing. Aftereffects of a similar magnitude are obtained when adapting and test images are both either upright or inverted, or for an upright adapter and an inverted test; but aftereffects are smaller when the adapter is inverted and the test upright. This pattern of results suggests that the face-distortion aftereffect is mediated by object-processing mechanisms including, but not restricted to, configurational face-processing mechanisms.

Movement Aftereffects and Figural Aftereffects

Recent work on certain movement aftereffects has shown that the duration of such effects is greater in the lower half of the visual field than it is in the upper half. This finding is said to be opposed to the theory of figural aftereffects developed by Koehler and Wallach. Closer examination of the situation shows that the new facts agree with the theory.

Extraversion and Duration of the Archimedes Spiral Aftereffect

Two studies are reported testing the relationship between reported duration of the Archimedes Spiral Aftereffect (SAE) and the interaction between the personality variables of neuroticism and extraversion as measured by Eysenck's MPI. In both studies SAE was related to an interaction between neuroticism and extraversion, but in opposite directions in each. Because of the different attitudes toward Ss' task in the two studies, it was concluded that the personality variables interacted with each other and with a third variable, that of “task-motivation.”

A Re-Examination of Kinesthetic Figural Aftereffects in the Brain-Injured

Kinesthetic figural aftereffects (KFAE) were measured on 46 brain-damaged and 24 control Ss, following the method of Klein and Krech (K&K). Although occasional trends in the data were consistent with K&K's finding that brain-injured Ss are more susceptible to KFAE, most of the data did not clearly corroborate their earlier finding to a statistically convincing degree, even though a larger number of Ss was used in this study than in K&K's.

Procedural Considerations of the Spiral Aftereffect Test

In Exp. I durations of the aftereffects under the conditions of successive observations of an expanding spiral, successive observations of a contracting spiral, and alternate observations of an expanding and a contracting spiral indicated that alternate observation of an expanding and a contracting spiral yielded spiral aftereffects (SAEs) of shorter duration for both spirals than did successive observations of each spiral alone. The mean duration of the SAE for the non-alternating condition exceeded that for the alternating condition by 4.07 sec. (42%) for the expanding spiral and 3.17 sec. (20%) for the contracting spiral. The contracting spiral yielded SAEs of longer duration than did the expanding spiral under both the conditions of alternation and non-alternation and by about the same absolute amount. No change is expected from repeated exposure to the SAE test, since there was no significant change from the first to the third block of 40 trials. In Exp. II the effect of the width of the spiral on the duration of aftereffect was studied under conditions of successive observations of an expanding and a contracting spiral. Results showed that a spiral composed of equal parts black and white yielded SAEs of longer duration than did a spiral of 25% black and 75% white, or 75% black and 25% white.

Reliability of Duration as a Measure of the Spiral Aftereffect

Data supported the reliability of duration as a measure of the spiral aftereffect and showed that a contracting spiral was judged more reliably than an expanding one.

On the Interpretation of “Interocular Transfer”

Terwilliger has recently presented further evidence for the “interocular transfer” of after-images and suggests that figural aftereffects which also “transfer” may therefore also be retinal. Terwilliger's interpretation is questioned on the ground that “transfer” means two quite different things for these two phenomena.

Induced Colors and Colors Produced by Chromatic Illumination May Have Similar Physiological Bases

Thirteen Os obtained afterimages of each of two targets. The “induced” target was a green ring surrounding an achromatic (but phenomenally magenta) disk; the “neutralized” target was the same as the induced one, except that chromatic green illumination was added to the disk so as to make it phenomenally achromatic. Two findings support the conjecture that the retinal process underlying perception of induced colors is similar to that underlying perception of colors produced by chromatic illumination: (1) an induced magenta can be mixed with a green produced by chromatic illumination so as to yield a phenomenally neutral color, and (2) the green in the afterimage of the disk in the induced target was more saturated than the green in the afterimage of the disk in the neutralized target.

Some Laboratory Measures of Extraversion-Introversion

The Maudsley Personality Inventory was given to a pool of 309 Ss from which three groups were selected along the extraversion dimension, two to represent each extreme (extravert N = 20, introvert N = 19), and an intermediate group ( N = 19). The three groups were equated for neuroticism. Ss were tested on the following measures: time-judgment, breath-holding, digit repetition, line reproduction, leg persistence, set change, kinaesthetic figural after-effect, and size constancy. Extraverts were superior in breath-holding, had a longer time span in digit repetition, showed longer leg persistence, greater variability in line reproduction, a tendency to underestimation in time judgment, but were inferior in arithmetic computation under slow set change conditions. No significant difference between extraverts and introverts was observed in the kinaesthetic figural after-effect or in size constancy.

Asymmetry of Aftereffects in the Upper and Lower Visual Fields

The movement aftereffect was used to study the asymmetry of aftereffects in the median plane. The results show significantly greater aftereffects in the lower part of the visual field as compared with the upper part. These results are inconsistent with the Koehler-Wallach proposals concerning asymmetry but are consistent with the metabolic hypotheses of Wertheimer.

Tracking Rotary Motion After-Effect with Different Illuminations of Inspection and Test Fields

Taylor's psychophysical theory of figural after-effects was used to predict the effect of changes in illumination of inspection and test fields on the amount and the rate of decay of the rotary motion after-effect. As predicted, the brighter inspection disc produced more after-effect, while the brighter test disc produced a smaller and faster-decaying after-effect.

Bodily Activity and Perceptual Activity

This report describes the results of 2 studies designed to test the hypothesis that there is an inverse relation between bodily and perceptual activity. In Study I 100 college students' bodily movements were recorded by kymograph while they were tested for the autokinetic illusion, reversible figure-ground, Necker cube reversals, and visual figural aftereffects. No significant correlations were found between bodily movement and perceptual scores. Study II involved only autokinetic illusion scores and induced bodily activity of 200 Ss. Significant linear correlations were found in the expected direction, i.e., bodily movement correlated positively with autokinetic latency in both males and females; bodily movement was negatively correlated with extent of autokinetic movement in females. Female Ss in both studies showed significantly greater autokinetic latency than males.

Effects of Temporal Order of Stimulus Presentation on the Direction of Figural Aftereffects

An investigation into the aftereffects of simultaneously presented parallel contours was carried out to demonstrate the attraction of these contours. These attraction effects contrasted significantly with the repulsion effects obtained in the orthodox figural-aftereffect situation. An interpretation was offered in terms of the interaction of separate processes of primary adaptation and in terms of more complex processes of temporal comparison.

Gamma Movement: Apparent Movement in Figural Aftereffects Experiments

Standard contour circles, 40 mm. in diameter, were tachistoscopically presented for 1 sec. With each presentation, .8 sec. after the onset, one of a number of comparison circles, varying in diameter from 32 to 48 mm., was presented alongside for .2 sec. Those comparison circles which were equal to and slightly smaller than the standard circles were judged larger significantly more often than chance. Thus, the initial phase of gamma movement, the apparent expansion of briefly exposed figures, was elicited under conditions comparable to those of some figural aftereffect experiments.

Viewing Distance and the Aftereffects of Fixation

In a previous experiment, a fixated three-dimensional object was shown to recede from the position it held prior to fixation. Since this phenomenon may be accounted for in terms of a visual compensation for the strain of convergence during prolonged fixation, it was expected that fixation of a near figure would result in a greater aftereffect than fixation of a far figure. The results of this study indicated that, while there was a greater frequency of expected aftereffects with the near figures, there was also a greater frequency of reversed aftereffects with the far figures. The latter finding raised problems of an interpretation of the theory under consideration, the implications of which were discussed.

Duration of Spiral Aftereffect as a Function of Retinal Size, Retinal Place, and Hemiretinal Transfer

This experiment has shown that, although both rods and cones mediate the spiral aftereffect, cone areas give a larger response. Increasing size of the retinal image results in longer durations of SAE but rods are more affected by this increase than are cones. There is a general weakening in aftereffect resulting from “transfer” from one hemiretina to another with cone areas showing greater loss than rod areas. Size of retinal image has been shown to be a potent variable and, in fact, under some small size conditions, normal Ss fail to observe any effect whatsoever. In view of these findings, it is apparent that size of retinal image is a variable which must be carefully controlled if comparable results are to be obtained. Review of the clinical literature, however, reveals that distance from S to spiral and objective spiral size often vary from experiment to experiment. This variation could well account for some of the differences in results of clinical studies. It is proposed that a standard spiral size and testing distance be introduced for clinical use.

Massed Practice and Motion After-Effect

No significant change in the duration of motion after-effect was found in 20 massed trials using a rotating windmill stimulus pattern. However, there was a reliable tendency for each S to repeat his performance on 2 separate days, either to shorten or to lengthen the after-effect during the session.

Duration as a Measure of the Spiral Aftereffect

The purpose of this experiment was to study the reliability of duration as a measure of the spiral aftereffect. The results for 10 Ss indicate that duration is a highly reliable measure and that duration is a simple monotonic function of exposure-time.

Kinesthetic Aftereffects are in the Hands, Not in Phenomenal Space

Kinesthetic figural aftereffects (KFAE) were measured in 44 Ss to determine whether satiation occurs in the hands or in phenomenal three-dimensional space. KFAE of equal sign and magnitude occurred in the hands handling the satiation objects whether the arms were crossed or uncrossed during the satiation period. Therefore the satiation effect is in the hands, not in phenomenal space.

Adaptation to Spiral Motion in Crowding Condition

When a single, moving stimulus is presented in the peripheral visual field, its direction of motion can be easily distinguished, but when the same stimulus is flanked by other similar moving stimuli, observers are unable to report its direction of motion. In this condition, known as ‘crowding’, specific features of visual stimuli do not access conscious perception. The aim of this study was to investigate whether adaptation to spiral motion is preserved in crowding conditions. Logarithmic spirals were used as adapting stimuli. A rotating spiral stimulus (target spiral) was presented, flanked by spirals of the same type, and observers were adapted to its motion. The observers' task was to report the rotational direction of a directionally ambiguous motion (test stimulus) presented afterwards. The directionally ambiguous motion consisted of a pair of spirals flickering in counterphase, which were mirror images of the target spiral. Although observers were not aware of the rotational direction of the target and identified it at chance levels, the direction of rotation reported by the observers during the test phase (motion aftereffect) was contrarotational to the direction of the adapting spiral. Since all contours of the adapting and test stimuli were 90° apart, local motion detectors tuned to the directions of the mirror-image spiral should fail to respond, and therefore not adapt to the adapting spiral. Thus, any motion aftereffect observed should be attributed to adaptation of global motion detectors (ie rotation detectors). Hence, activation of rotation-selective cells is not necessarily correlated with conscious perception.

Heads First: Visual Aftereffects Reveal Hierarchical Integration of Cues to Social Attention

Determining where another person is attending is an important skill for social interaction that relies on various visual cues, including the turning direction of the head and body. This study reports a novel high-level visual aftereffect that addresses the important question of how these sources of information are combined in gauging social attention. We show that adapting to images of heads turned 25° to the right or left produces a perceptual bias in judging the turning direction of subsequently presented bodies. In contrast, little to no change in the judgment of head orientation occurs after adapting to extremely oriented bodies. The unidirectional nature of the aftereffect suggests that cues from the human body signaling social attention are combined in a hierarchical fashion and is consistent with evidence from single-cell recording studies in nonhuman primates showing that information about head orientation can override information about body posture when both are visible.

[MOTION AFTEREFFECT AS A UNIVERSAL PHENOMENON IN SENSORY SYSTEMS INVOLVED IN SPACE ORIENTATION. II. AUDITORY MOTION AFTEREFFECT]

Adaptation to sound source motion can cause noticeable changes in spatial perception of the following sound stimuli. Neural mechanisms of selective sensitivity to motion are the basis of this phenomenon, called the auditory motion aftereffect. The auditory motion aftereffects were demonstrated under different stimulation conditions, both after the presentation of different motion models and in the real sound source motion. The auditory aftereffects are specifically characterized by its spatial and frequency selectivity as well as by the optimal motion velocity at which the effect is maximal. These features and the presence of the intersensory motion adaptation effects indicate a common nature of the auditory and visual motion aftereffects and allow suggesting the existence of the common system of motion adaptation for different modalities that provide spatial orientation.

Adding years to your life (or at least looking like it): a simple normalization underlies adaptation to facial age

Adaptation has been widely used to probe how experience shapes the visual encoding of faces, but the pattern of perceptual changes produced by adaptation and the neural mechanisms these imply remain poorly characterized. We explored how adaptation alters the perceived age of faces, a fundamental facial attribute which can uniquely and reliably be scaled by observers. This allowed us to measure how adaptation to one age level affected the full continuum of perceived ages. Participants guessed the ages of faces ranging from 18-89, before or after adapting to a different set of faces composed of younger, older, or middle-aged adults. Adapting to young or old faces induced opposite linear shifts in perceived age that were independent of the model's age. Specifically, after adapting to younger or older faces, faces of all ages appeared 2 to 3 years older or younger, respectively. In contrast, middle-aged adaptors induced no aftereffects. This pattern suggests that adaptation leads to a simple and uniform renormalization of age perception, and is consistent with a norm-based neural code for the mechanisms mediating the perception of facial age.

[Motion aftereffect as a universal phenomenon for sensory systems involved in orientation in space. I. Visual aftereffects]

At present there are serious grounds to believe that motion aftereffect is characteristic for all sensory systems involved in spatial orientation, and that adaptation to movement in one sensory system causes changes in another one and that such adjustment is of critical adaptive significance. In this part of the review there are briefly presented developments and the current state of studies on this issue in visual modality. The visual motion aftereffect has been studied considerably more completely as compared with other modalities. The main concepts about mechanisms of this phenomenon and employment of adaptation to motion in studies of visual analysis of movement at its different levels are actively used in the current scientific literature to understand mechanisms of this phenomenon in other sensory systems. The leading role of vision for orientation in space is manifested in the multimodal interaction where visual adaptation to movement produces significant changes of perception in other modalities.

The spiral aftereffect technique (SAT) can differentiate between depressive and somatoform disorder patients

This study examined how differences in visuo-perceptual patterns are related to psychopathology. Fifty-six patients (37 women, 19 men; M age = 43.8 yr., SD = 13.4) with a main diagnosis of unipolar depression and 42 patients (22 women, 20 men; M age = 42.0 yr., SD = 11.1) with a main diagnosis of somatoform disorder were compared. The duration and trend of a visual motion aftereffect were measured with the Spiral Aftereffect Technique (SAT). The results indicated that successively increasing aftereffect durations characterized the depressive patients, whereas patterns of very short or short final aftereffect preceded by successively decreasing aftereffect durations characterized the patients with a somatoform disorder. The SAT is thus a valuable tool for linking objectively measured perceptual-personality characteristics with some mental disorders.

Decision-dependent aftereffects for faces

Adaptation-related aftereffects (AEs) have been found in the perception of face identity, in that perception of an ambiguous face is typically biased away from the identity of a preceding unambiguous adaptor face. In previous studies, we could show that both perceptual ambiguity and physical similarity play a role in determining perceived face identity AEs, Cortex 49 (2013) 1963-1977, Plos One 8 (2013) e70525. Here, we tested further the role of ambiguity by manipulating participants' task such that the very same target stimuli were either ambiguous or unambiguous regarding stimulus classification. We created two partially overlapping continua spanning three unfamiliar face identities each, by morphing identity A via B to C, and B via C to D. In a first session, participants were familiarised with faces A and C and asked to classify faces of the A-B-C continuum as either identity A or C in an AE paradigm. Following adaptation to A or C, we observed contrastive AEs for the ambiguous identity B, but not for the unambiguous identities A or C. In a second session, the same participants were familiarised with faces B and D, followed by tests of AEs for the B-C-D continuum now involving a B-D classification task. We again observed contrastive AEs but only for target identity C (ambiguous for the decision) and not for B or D (unambiguous). Our results suggest that perceptual ambiguity, as given by the task-context, determines whether or not AEs are induced.

High-level aftereffects to global scene properties

Adaptation is ubiquitous in the human visual system, allowing recalibration to the statistical regularities of its input. Previous work has shown that global scene properties such as openness and mean depth are informative dimensions of natural scene variation useful for human and machine scene categorization (Greene & Oliva, 2009b; Oliva & Torralba, 2001). A visual system that rapidly categorizes scenes using such statistical regularities should be continuously updated, and therefore is prone to adaptation along these dimensions. Using a rapid serial visual presentation paradigm, we show aftereffects to several global scene properties (magnitude 8-21%). In addition, aftereffects were preserved when the test image was presented 10 degrees away from the adapted location, suggesting that the origin of these aftereffects is not solely due to low-level adaptation. We show systematic modulation of observers' basic-level scene categorization performances after adapting to a global property, suggesting a strong representational role of global properties in rapid scene categorization.

Inhibitory competition between shape properties in figure-ground perception

Theories of figure-ground perception entail inhibitory competition between either low-level units (edge or feature units) or high-level shape properties. Extant computational models instantiate the 1st type of theory. The authors investigated a prediction of the 2nd type of theory: that shape properties suggested on the ground side of an edge are suppressed when they lose the figure-ground competition. In Experiment 1, the authors present behavioral evidence of the predicted suppression: Object decisions were slower for line drawings that followed silhouettes suggesting portions of objects from the same rather than a different category on their ground sides. In Experiment 2, the authors reversed the silhouette's figure-ground relationships and obtained speeding rather than slowing in the same category condition, thereby demonstrating that the Experiment 1 results reflect suppression of those shape properties that lose the figure-ground competition. These experiments provide the first clear empirical evidence that figure-ground perception entails inhibitory competition between high-level shape properties and demonstrate the need for amendments to existing computational models. Furthermore, these results suggest that figure-ground perception may itself be an instance of biased competition in shape perception.