A functional explanation for the effects of visual exposure on preference

Visual exposure to an object can modulate an observer's degree of preference for it, initially enhancing preference (a 'familiarity preference' regime), and eventually lowering it again (a 'novelty preference' regime). Here we investigate whether there may be a functional advantage to modulating preference in this way. We put forth the simple hypothesis that degree of preference for an object of type X is the brain's estimate of the expected utility of acting to obtain X. In the light of this view of what preferences fundamentally represent, we are able to explain the 'exposure effect' and many of the connected phenomena.

Dynamic effects and information quantifiers of statistical memory of MEG's signals at photosensitive epilepsy

The time series analysis of magnetoencephalographic (MEG) signals is very important both for basic brain research and for medical diagnosis and treatment. Here we discuss the crucial role of statistical memory effects (ME) in human brain functioning with photosensitive epilepsy (PSE). We study two independent statistical memory quantifiers that reflect the dynamical characteristics of neuromagnetic brain responses on a flickering stimulus of different colored combinations from a group of control subjects, which are contrasted with those from a patient with PSE. We analyze the frequency dependence of two memory measures for the neuromagnetic signals. The strong memory and the accompanying transition to a regular and robust regime of the signals' chaotic behavior in the separate areas are characteristic for a patient with PSE. This particularly interesting observation most likely identifies the regions of the protective mechanism in a human organism against occurrence of PSE.

"X-ray vision" and the evolution of forward-facing eyes

Why do our eyes face forward, and why do many mammals have eyes facing sideways? Here, we describe results suggesting that the degree of binocular convergence is selected to maximize how much the mammal can see in its environment. Mammals in non-cluttered environments can see the most around them with panoramic, laterally directed eyes. Mammals in cluttered environments, however, can see best when their eyes face forward, for binocularity has the power of "seeing through" clutter out in the world. Evidence across mammals closely fits the predictions of this "X-ray" hypothesis.

Self and world: large scale installations at science museums

This paper describes three examples of illusion installation in a science museum environment from the author's collaboration with the artist and architect. The installations amplify the illusory effects, such as vection (visually-induced sensation of self motion) and motion-induced blindness, to emphasize that perception is not just to obtain structure and features of objects, but rather to grasp the dynamic relationship between the self and the world. Scaling up the size and utilizing the live human body turned out to be keys for installations with higher emotional impact.

Electronically switchable sham transcranial magnetic stimulation (TMS) system

Transcranial magnetic stimulation (TMS) is increasingly being used to demonstrate the causal links between brain and behavior in humans. Further, extensive clinical trials are being conducted to investigate the therapeutic role of TMS in disorders such as depression. Because TMS causes strong peripheral effects such as auditory clicks and muscle twitches, experimental artifacts such as subject bias and placebo effect are clear concerns. Several sham TMS methods have been developed, but none of the techniques allows one to intermix real and sham TMS on a trial-by-trial basis in a double-blind manner. We have developed an attachment that allows fast, automated switching between Standard TMS and two types of control TMS (Sham and Reverse) without movement of the coil or reconfiguration of the setup. We validate the setup by performing mathematical modeling, search-coil and physiological measurements. To see if the stimulus conditions can be blinded, we conduct perceptual discrimination and sensory perception studies. We verify that the physical properties of the stimulus are appropriate, and that successive stimuli do not contaminate each other. We find that the threshold for motor activation is significantly higher for Reversed than for Standard stimulation, and that Sham stimulation entirely fails to activate muscle potentials. Subjects and experimenters perform poorly at discriminating between Sham and Standard TMS with a figure-of-eight coil, and between Reverse and Standard TMS with a circular coil. Our results raise the possibility of utilizing this technique for a wide range of applications.

Adapting to an aftereffect

We report a new type of orientation-contingent color aftereffect in which the color aftereffect is opposite to the classical McCollough effect, i.e., the perceived color of the aftereffect is the same as the inducer's color. Interleaved exposure to red, horizontal and achromatic (gray), horizontal gratings led to a long-lasting aftereffect in which achromatic horizontal gratings appeared reddish. The effect, termed the anti-McCollough effect, although weaker than the classical aftereffect, remained stable for a moderate duration of time (24 hours). Unlike the classical aftereffect, which is known to not transfer interocularly, the new after-aftereffect transferred 100%, suggesting that its locus in the brain was downstream of the classical effect. It is likely that neurons in a higher-order area adapted to the classical color aftereffect that was represented in a lower-order area, thus forming an aftereffect of an aftereffect, i.e., an after-aftereffect. Our finding has implications as to how neural activity in lower- and higher-level areas in the brain interacts to yield conscious visual experience.

Distortions of subjective time perception within and across senses

BACKGROUND

The ability to estimate the passage of time is of fundamental importance for perceptual and cognitive processes. One experience of time is the perception of duration, which is not isomorphic to physical duration and can be distorted by a number of factors. Yet, the critical features generating these perceptual shifts in subjective duration are not understood.

METHODOLOGY/FINDINGS

We used prospective duration judgments within and across sensory modalities to examine the effect of stimulus predictability and feature change on the perception of duration. First, we found robust distortions of perceived duration in auditory, visual and auditory-visual presentations despite the predictability of the feature changes in the stimuli. For example, a looming disc embedded in a series of steady discs led to time dilation, whereas a steady disc embedded in a series of looming discs led to time compression. Second, we addressed whether visual (auditory) inputs could alter the perception of duration of auditory (visual) inputs. When participants were presented with incongruent audio-visual stimuli, the perceived duration of auditory events could be shortened or lengthened by the presence of conflicting visual information; however, the perceived duration of visual events was seldom distorted by the presence of auditory information and was never perceived shorter than their actual durations.

CONCLUSIONS/SIGNIFICANCE

These results support the existence of multisensory interactions in the perception of duration and, importantly, suggest that vision can modify auditory temporal perception in a pure timing task. Insofar as distortions in subjective duration can neither be accounted for by the unpredictability of an auditory, visual or auditory-visual event, we propose that it is the intrinsic features of the stimulus that critically affect subjective time distortions.

Dynamic perceptual changes in audiovisual simultaneity

BACKGROUND

The timing at which sensory input reaches the level of conscious perception is an intriguing question still awaiting an answer. It is often assumed that both visual and auditory percepts have a modality specific processing delay and their difference determines perceptual temporal offset.

METHODOLOGY/PRINCIPAL FINDINGS

Here, we show that the perception of audiovisual simultaneity can change flexibly and fluctuates over a short period of time while subjects observe a constant stimulus. We investigated the mechanisms underlying the spontaneous alternations in this audiovisual illusion and found that attention plays a crucial role. When attention was distracted from the stimulus, the perceptual transitions disappeared. When attention was directed to a visual event, the perceived timing of an auditory event was attracted towards that event.

CONCLUSIONS/SIGNIFICANCE

This multistable display illustrates how flexible perceived timing can be, and at the same time offers a paradigm to dissociate perceptual from stimulus-driven factors in crossmodal feature binding. Our findings suggest that the perception of crossmodal synchrony depends on perceptual binding of audiovisual stimuli as a common event.

Spatial contexts can inhibit a mislocalization of visual stimuli during smooth pursuit

The position of a flash presented during pursuit is mislocalized in the direction of the pursuit. Although this has been explained by a temporal mismatch between the slow visual processing of flash and fast efferent signals on eye positions, here we show that spatial contexts also play an important role in determining the flash position. We put various continuously lit objects (walls) between veridical and to-be-mislocalized positions of flash. Consequently, these walls significantly reduced the mislocalization of flash, preventing the flash from being mislocalized beyond the wall (Experiment 1). When the wall was shortened or had a hole in its center, the shape of the mislocalized flash was vertically shortened as if cutoff or funneled by the wall (Experiment 2). The wall also induced color interactions; a red wall made a green flash appear yellowish if it was in the path of mislocalization (Experiment 3). Finally, those flash-wall interactions could be induced even when the walls were presented after the disappearance of flash (Experiment 4). These results indicate that various features (position, shape, and color) of flash during pursuit are determined with an integration window that is spatially and temporally broad, providing a new insight for generating mechanisms of eye-movement mislocalizations.

Direct instrumental conditioning of neural activity using functional magnetic resonance imaging-derived reward feedback

Successful learning is often contingent on feedback. In instrumental conditioning, an animal or human learns to perform specific responses to obtain reward. Instrumental conditioning is often used by behavioral psychologists to train an animal (or human) to produce a desired behavior. Shaping involves reinforcing those behaviors, which in a stepwise manner are successively closer to the desired behavior until the desired behavior is reached. Here, we aimed to extend this traditional approach to directly shape neural activity instead of overt behavior. To achieve this, we scanned 22 human subjects with functional magnetic resonance imaging and performed image processing in parallel with acquisition. We delineated regions of interest (ROIs) in finger and toe motor/somatosensory regions and used an instrumental shaping procedure to induce a regionally specific increase in activity by providing an explicit monetary reward to reinforce neural activity in the target areas. After training, we found a significant and regionally specific increase in activity in the ROI being rewarded (finger or toe) and a decrease in activity in the nonrewarded region. This demonstrates that instrumental conditioning procedures can be used to directly shape neural activity, even without the production of an overt behavioral response. This procedure offers an important alternative to traditional biofeedback-based approaches and may be useful in the development of future therapies for stroke and other brain disorders.

Interrupting the cascade: Orienting contributes to decision making even in the absence of visual stimulation

Most systematic studies of human decision making approach the subject from a cost analysis point of view and assume that people make the highest utility choice. Very few articles investigate subjective decision making, such as that involving preference, although such decisions are very important for our daily functioning. We have argued (Shimojo, Simion, Shimojo, & Scheier, 2003) that an orienting bias effectively leads to the preference decision by means of a positive feedback loop involving mere exposure and preferential looking. The illustration of this process is a continually increasing gaze bias toward the eventual choice, which we call the gaze cascade effect. In the present study, we interrupt the natural process of preference selection, but we show that gaze behavior does not change even when the stimuli are removed from observers' visual field. This demonstrates that once started, the involvement of orienting in decision making cannot be stopped and that orienting acts independently of the presence of visual stimuli. We also show that the cascade effect is intrinsically linked to the decision itself and is not triggered simply by a tendency to look at preferred targets.

Dynamical evolution of motion perception

Motion is defined as a sequence of positional changes over time. However, in perception, spatial position and motion dynamically interact with each other. This reciprocal interaction suggests that the perception of a moving object itself may dynamically evolve following the onset of motion. Here, we show evidence that the percept of a moving object systematically changes over time. In experiments, we introduced a transient gap in the motion sequence or a brief change in some feature (e.g., color or shape) of an otherwise smoothly moving target stimulus. Observers were highly sensitive to the gap or transient change if it occurred soon after motion onset (< or =200 ms), but significantly less so if it occurred later (> or = 300 ms). Our findings suggest that the moving stimulus is initially perceived as a time series of discrete potentially isolatable frames; later failures to perceive change suggests that over time, the stimulus begins to be perceived as a single, indivisible gestalt integrated over space as well as time, which could well be the signature of an emergent stable motion percept.

Bare skin, blood and the evolution of primate colour vision

We investigate the hypothesis that colour vision in primates was selected for discriminating the spectral modulations on the skin of conspecifics, presumably for the purpose of discriminating emotional states, socio-sexual signals and threat displays. Here we show that, consistent with this hypothesis, there are two dimensions of skin spectral modulations, and trichromats but not dichromats are sensitive to each. Furthermore, the M and L cone maximum sensitivities for routine trichromats are optimized for discriminating variations in blood oxygen saturation, one of the two blood-related dimensions determining skin reflectance. We also show that, consistent with the hypothesis, trichromat primates tend to be bare faced.

Development of multisensory spatial integration and perception in humans

Previous studies have shown that adults respond faster and more reliably to bimodal compared to unimodal localization cues. The current study investigated for the first time the development of audiovisual (A-V) integration in spatial localization behavior in infants between 1 and 10 months of age. We observed infants' head and eye movements in response to auditory, visual, or both kinds of stimuli presented either 25 degrees or 45 degrees to the right or left of midline. Infants under 8 months of age intermittently showed response latencies significantly faster toward audiovisual targets than toward either auditory or visual targets alone They did so, however, without exhibiting a reliable violation of the Race Model, suggesting that probability summation alone could explain the faster bimodal response. In contrast, infants between 8 and 10 months of age exhibited bimodal response latencies significantly faster than unimodal latencies for both eccentricity conditions and their latencies violated the Race Model at 25 degrees eccentricity. In addition to this main finding, we found age-dependent eccentricity and modality effects on response latencies. Together, these findings suggest that audiovisual integration emerges late in the first year of life and are consistent with neurophysiological findings from multisensory sites in the superior colliculus of infant monkeys showing that multisensory enhancement of responsiveness is not present at birth but emerges later in life.

Discrete color filling beyond luminance gaps along perceptual surfaces

Perceived color at a point in space is not determined simply by the color directly stimulating the corresponding retinal position. Surface color is informed by flanking edge signals, which also serve to inhibit the intrusion of signals from neighboring surfaces. Spatially continuous local interactions among color and luminance signals have been implicated in a propagation process often referred to as filling-in. Here, we report a phenomenon of discrete color filling whereby color jumps over luminance gaps filling into disconnected regions of the stimulus. This color filling is found to be blocked at boundaries defined by texture. The color filling is also highly specific to the elements belonging to a common perceptual surface, even when multiple surfaces are transparently overlaid. Our results indicate that color filling can be governed by a host of visual cues outside the realm of first-order color and brightness, via their impact on perceptual surface segmentation and segregation.

Early interactions between orienting, visual sampling and decision making in facial preference

Decision making has been regarded as the last stage before action in the human information processing, certainly subsequent to sensory sampling and perceptual integration. Our latest study showed that orienting contributes to preference decision making, by integrating preferential looking and mere exposure in a positive feedback loop leading to the conscious choice. Here, we introduce a gaze-contingent window method of stimulus presentation into our experimental paradigm, to completely block holistic stimulus processing while preserving piecemeal sampling through the gaze-contingent "peephole". This effectively zooms the visual processing in time domain, allowing us to show that orienting and decision making can interact long before the actual conscious choice. The finding also suggests that this interaction is independent of holistic properties of face stimuli and can be totally memory-driven.

Development of multisensory spatial integration and perception in humans

Previous studies have shown that adults respond faster and more reliably to bimodal compared to unimodal localization cues. The current study investigated for the first time the development of audiovisual (A-V) integration in spatial localization behavior in infants between 1 and 10 months of age. We observed infants' head and eye movements in response to auditory, visual, or both kinds of stimuli presented either 25 degrees or 45 degrees to the right or left of midline. Infants under 8 months of age intermittently showed response latencies significantly faster toward audiovisual targets than toward either auditory or visual targets alone They did so, however, without exhibiting a reliable violation of the Race Model, suggesting that probability summation alone could explain the faster bimodal response. In contrast, infants between 8 and 10 months of age exhibited bimodal response latencies significantly faster than unimodal latencies for both eccentricity conditions and their latencies violated the Race Model at 25 degrees eccentricity. In addition to this main finding, we found age-dependent eccentricity and modality effects on response latencies. Together, these findings suggest that audiovisual integration emerges late in the first year of life and are consistent with neurophysiological findings from multisensory sites in the superior colliculus of infant monkeys showing that multisensory enhancement of responsiveness is not present at birth but emerges later in life.

Cyclopean flash-lag illusion

Possible physiological mechanisms to explain the flash-lag effect, in which subjects perceive a flashed item that is co-localized with a moving item as trailing behind the moving item, have been found within the retina of lower species, and in the motor pathways of humans. Here, we demonstrate flash-lag employing "second-order" moving and flashed stimuli, defined solely by their binocular-disparity, to circumvent any possible "early" contributions to the effect. A significant flash-lag effect was measured with cyclopean stimuli composed entirely of correlated random dot patterns. When the disparity-defined moving stimulus was replaced with a luminance-defined one, potentially engaging retinal mechanisms, the magnitude of the measured effect showed no significant change. Thus, in primates, though retinal mechanisms may contribute, flash-lag must be explained through cortical processes.

Is avoiding an aversive outcome rewarding? Neural substrates of avoidance learning in the human brain

Avoidance learning poses a challenge for reinforcement-based theories of instrumental conditioning, because once an aversive outcome is successfully avoided an individual may no longer experience extrinsic reinforcement for their behavior. One possible account for this is to propose that avoiding an aversive outcome is in itself a reward, and thus avoidance behavior is positively reinforced on each trial when the aversive outcome is successfully avoided. In the present study we aimed to test this possibility by determining whether avoidance of an aversive outcome recruits the same neural circuitry as that elicited by a reward itself. We scanned 16 human participants with functional MRI while they performed an instrumental choice task, in which on each trial they chose from one of two actions in order to either win money or else avoid losing money. Neural activity in a region previously implicated in encoding stimulus reward value, the medial orbitofrontal cortex, was found to increase, not only following receipt of reward, but also following successful avoidance of an aversive outcome. This neural signal may itself act as an intrinsic reward, thereby serving to reinforce actions during instrumental avoidance.

The structures of letters and symbols throughout human history are selected to match those found in objects in natural scenes

Are there empirical regularities in the shapes of letters and other human visual signs, and if so, what are the selection pressures underlying these regularities? To examine this, we determined a wide variety of topologically distinct contour configurations and examined the relative frequency of these configuration types across writing systems, Chinese writing, and nonlinguistic symbols. Our first result is that these three classes of human visual sign possess a similar signature in their configuration distribution, suggesting that there are underlying principles governing the shapes of human visual signs. Second, we provide evidence that the shapes of visual signs are selected to be easily seen at the expense of the motor system. Finally, we provide evidence to support an ecological hypothesis that visual signs have been culturally selected to match the kinds of conglomeration of contours found in natural scenes because that is what we have evolved to be good at visually processing.

Touch-induced visual illusion

Although vision is considered the dominant modality, recent studies demonstrate the influence of other modalities on visual perception. For example, in the sound-induced flash illusion, two auditory stimuli cause one visual flash to be perceived as two. We report an extension of the sound-induced flash illusion to the tactile-visual domain, yielding the touch-induced flash illusion. Observers reported seeing two flashes on the majority of trials when a single flash was presented concurrently with two task-irrelevant brief tactile stimuli. Somatosensory stimulation changed the sensitivity (d') of detecting visual stimuli, which suggests that the observed effect is at least partly due to perceptual interactions. Together with other recent findings, these results challenge the notion that the processing of visual information is independent of activity in other modalities.