Illusory Perception Research Articles

Susceptibility to a multisensory speech illusion in older persons is driven by perceptual processes

Recent studies suggest that multisensory integration is enhanced in older adults but it is not known whether this enhancement is solely driven by perceptual processes or affected by cognitive processes. Using the “McGurk illusion,” in Experiment 1 we found that audio-visual integration of incongruent audio-visual words was higher in older adults than in younger adults, although the recognition of either audio- or visual-only presented words was the same across groups. In Experiment 2 we tested recall of sentences within which an incongruent audio-visual speech word was embedded. The overall semantic meaning of the sentence was compatible with either one of the unisensory components of the target word and/or with the illusory percept. Older participants recalled more illusory audio-visual words in sentences than younger adults, however, there was no differential effect of word compatibility on recall for the two groups. Our findings suggest that the relatively high susceptibility to the audio-visual speech illusion in older participants is due more to perceptual than cognitive processing.

Undecidability and opacity of metacognition in animals and humans.

Undecidability and opacity of metacognition in animals and humans.

Music Modulates the Strength of Vection

We presented four types of music (two fast tempo and two slow tempo types) during illusory self-motion perception (vection). Vection was induced by expansional dots (optic flow), and participants estimated its strength via magnitude estimation and by pressing a button. Our purpose of this study is to examine whether music alter vection strength. Results showed that vection was facilitated by two fast tempo types and one slow tempo type of music in lieu of a no-music condition. We speculated that fast tempo, active music might induce higher arousal levels in participants compared with a no-music condition, and that higher arousal levels might induce stronger vection. We speculated that this auditory method of modulating vection strength can be utilized in the virtual reality environment.

I speak fast when I move fast: the speed of illusory self-motion (vection) modulates the speed of utterances

Speed of utterance is an important factor in smooth and efficient conversation. We report a technique to increase utterance speed and that might improve a speaker's impression and information efficiency in conversation. We used a visual display consisting of optic flows in a large visual field that induced participants' illusory self-motion perception (vection). The speed of vection corresponded to the speed of the optic flows. Using this method, we investigated whether vection speed affects utterance speed. We presented fast- and slow-moving optic flow stimuli while dynamically swapping random dots presented to participants, during which time the participants were asked to talk for 2 min. Results revealed that the utterance speed was significantly faster in the fast optic flow condition. Our method could be a stepping stone for establishing a technique of modulating speech speed effectively.

Effects of Additional Visual Oscillation on Vection under Voluntary Eye Movement Conditions—Retinal Image Motion is Critical in Vection Facilitation

Horizontal oscillation introduced into a visual inducer can enhance an observer's illusory perception of vertical self-motion induced by a vertically moving optic flow pattern. To examine the effects of increased retinal image motion on the facilitation of vection, vection strength was analysed under various stimulus conditions where the oscillation of the retinal image was determined both by the motion of the visual stimulus and the observer's eye movements. The results indicated that the facilitation of vection was regulated by the oscillation of the visual stimulus on the observer's retina rather than the stimulus oscillation per se. Thus, the current experiment clearly favours the hypothesis that increased retinal image motion plays a critical role in the facilitation of vection.

Visual Jitter Inhibits Roll Vection for an Upright Observer

It is widely known that visual jitter convoluted with an expanding optical flow can robustly enhance an observer's illusory perception of forward self-motion (eg Palmisano et al 2000 Perception 29 57-67). In the present investigation I examine the effects of visual jitter on visually induced self-rotation (roll vection). The results showed that the strength of roll vection was decreased under conditions where the visual jitter was convoluted into the rotating visual stimulus. Although the extent of the decrement differed according to the amplitude and direction of the jitter, visual jitters in any direction with any amplitude can significantly reduce vection strength, at least under the conditions examined in the present experiment. The perceptual process underlying jitter effects on vection is discussed in the context of visuo-vestibular conflict in perception of self-motion.

The role of numerical magnitude and order in the illusory perception of size and brightness.

Processing magnitudes constitutes a common experience across multiple dimensions, for example when one has to compare sizes, duration, numbers, sound height or loudness. From a cognitive point of view, however, it is still unclear whether all these experiences rely on a common system, or on distinct systems, with more or less strong associations. One particularly striking way of observing such interference between the spatial and numerical dimensions consists in eliciting a bias in size judgment through the mere perception of irrelevant numerical stimuli. In such experimental context though, two questions remain open. First, it is still unknown whether the direction of the bias is related to the magnitude of the number presented, or to their position in an ordinal sequence, and thus could be elicited by other non-numerical ordinal sequences such as letters of the alphabet. Second, it is still unclear whether the observed interactions generalize to other continuous dimension of magnitude such as brightness. In the study reported here, both letters and numbers were used in a size- and a brightness-reproduction task. We observed a dissociation between the two types of stimuli when reproducing size, the illusion being elicited solely by numbers. When reproducing brightness, however, neither the letters nor the numbers elicited a bias. These findings suggest that, while only numerical magnitude, and not letters, elicits a bias in size perception, the concurrent processing of magnitude and brightness does not bring about the same illusion, supporting the idea of a relative independence in the processing of these two dimensions.

Individual differences in the multisensory temporal binding window predict susceptibility to audiovisual illusions.

Human multisensory systems are known to bind inputs from the different sensory modalities into a unified percept, a process that leads to measurable behavioral benefits. This integrative process can be observed through multisensory illusions, including the McGurk effect and the sound-induced flash illusion, both of which demonstrate the ability of one sensory modality to modulate perception in a second modality. Such multisensory integration is highly dependent upon the temporal relationship of the different sensory inputs, with perceptual binding occurring within a limited range of asynchronies known as the temporal binding window (TBW). Previous studies have shown that this window is highly variable across individuals, but it is unclear how these variations in the TBW relate to an individual's ability to integrate multisensory cues. Here we provide evidence linking individual differences in multisensory temporal processes to differences in the individual's audiovisual integration of illusory stimuli. Our data provide strong evidence that the temporal processing of multiple sensory signals and the merging of multiple signals into a single, unified perception, are highly related. Specifically, the width of right side of an individuals' TBW, where the auditory stimulus follows the visual, is significantly correlated with the strength of illusory percepts, as indexed via both an increase in the strength of binding synchronous sensory signals and in an improvement in correctly dissociating asynchronous signals. These findings are discussed in terms of their possible neurobiological basis, relevance to the development of sensory integration, and possible importance for clinical conditions in which there is growing evidence that multisensory integration is compromised.

Illusory Double Epenthesis in the [s_V] Context among Japanese Listeners: An Exploratory Study

Previous studies showed that English listeners tend to hear an [s_V] segment with [_] a silent gap as [sCV], where [C] is an epenthetic stop consonant such as [t]. The present study found that Japanese listeners, whose native language disallows [CCV] but allows [CVCV], often perceive [s_V] as [sVCV]. It is suggested that such illusory double-epenthetic percepts are generated via a two-step process, i.e., the vowel of [s_V] triggers an epenthetic consonant before it, and the initial consonant [s] and the newly generated epenthetic consonant [C] sequentially aligned induce a vowel epenthesis [V] between them.

Bantams (Gallus gallus domesticus) also perceive a reversed Zöllner illusion

Although pigeons have been shown to be susceptible to several size and length illusions, other avian species have not been tested intensively for illusory perception. Here we report how bantams perceive the Zöllner figure, in which parallel lines look nonparallel due to short crosshatches superimposed on the lines. Watanabe et al. (Cognition 119:137-141, 2011) showed that pigeons, like humans, perceived parallel lines as nonparallel but that the orientation of subjective convergence was opposite to that of humans. We trained three bantams to peck at the narrower (or wider) of the two gaps at the end of a pair of nonparallel lines. After adapting them to target lines with randomly oriented crosshatches (which result in no apparent illusion to humans), we tested the bantams' responses on randomly inserted probe trials, in which crosshatches that should induce the standard Zöllner-like illusion for humans replaced the randomly oriented ones. The results suggested bantams, like pigeons, perceive a reversed Zöllner illusion.

The neural correlates of illusory face perception: An fMRI study

The neural correlates of illusory face perception: An fMRI study

The neural correlates of illusory face perception: An fMRI study

The neural correlates of illusory face perception: An fMRI study

Objective and subjective cognitive enhancing effects of mixed amphetamine salts in healthy people

Psychostimulants such as mixed amphetamine salts (MAS, brand name Adderall) are widely used for cognitive enhancement by healthy young people, yet laboratory research on effectiveness has yielded variable results. The present study assessed the effects of MAS in healthy young adults with an adequately powered double-blind cross-over placebo-controlled trial. We examined effects in 13 measures of cognitive ability including episodic memory, working memory, inhibitory control, convergent creativity, intelligence and scholastic achievement, with the goals of determining (1) whether the drug is at least moderately enhancing (Cohen's d >= .5) to some or all cognitive abilities tested, (2) whether its effects on cognition are moderated by baseline ability or COMT genotype, and (3) whether it induces an illusory perception of cognitive enhancement. The results did not reveal enhancement of any cognitive abilities by MAS for participants in general. There was a suggestion of moderation of enhancement by baseline ability and COMT genotype in a minority of tasks, with MAS enhancing lower ability participants on word recall, embedded figures and Raven's Progressive Matrices. Despite the lack of enhancement observed for most measures and most participants, participants nevertheless believed their performance was more enhanced by the active capsule than by placebo. We conclude that MAS has no more than small effects on cognition in healthy young adults, although users may perceive the drug as enhancing their cognition.This article is part of a Special Issue entitled ‘Cognitive Enhancers’.

Masking and color inheritance along the apparent motion path

Long-range apparent motion is the illusory motion that can be perceived when two static and distant stimuli are presented in succession. Within some spatiotemporal range not only is motion sensed, but it appears as if one stimulus is displaced from one place to another (termed beta or optimal motion). Several groups have found that this illusory percept can interact with perception of a physically present stimulus, but some disagree on the origin of these interactions. We know little about how suppressive effects depend on feature-similarity between a target and the stimuli in apparent motion (inducers)-which would indicate an early perceptual locus-or even about the minimal conditions under which to obtain this effect. Unlike early studies that used a two-stroke apparent motion paradigm, we were able to demonstrate that motion can mask stimuli presented at interpolated locations along the apparent motion path, as shown by the elevation of contrast thresholds compared to a control condition. Apparent motion masking depended on color similarity between target and inducers. Further, we found evidence that the color of inducers alters the apparent color of intervening gray probes, indicating some inheritance or chromatic averaging across distant locations, but no clear evidence of predictive updating. Finally, the analysis of the presentation times delivering maximal masking effects suggests a predictive interpolation process is responsible for interference by apparent motion filling-in. We discuss alternative mechanisms, in particular the possible role of apparent-motion-induced metacontrast masking in generating this pattern of results.

The rubber hand illusion modulates pseudoneglect

The rubber hand illusion (RHI) refers to the illusory perception of ownership of a rubber hand that may occur when covert tactile stimulation of a participant's hand co-occurs with overt corresponding stimulation of a rubber hand. It is proposed that integrating the rubber hand into one's body image may shift the subjective body midline away from the rubber hand. The present study investigated the influence of the RHI on pseudoneglect on the line bisection task, i.e. the leftward bias when marking the centre of horizontal lines, in 79 neurologically healthy adults. Overall, pseudoneglect was reduced after RHI application. Importantly, this effect was specific for individuals who reported having vividly experienced the illusion (high responders) as opposed to individuals who did not (low responders). Moreover, pseudoneglect was eliminated only after RHI application to the left hand. This pattern of results is consistent with functional hemispheric asymmetry for spatial processing and suggests that integrating the left sided rubber hand into one's body image shifts the subjective body midline to the right, thus counteracting pseudoneglect.

Unrecognized Changes in the Self Contribute to Exaggerated Judgments of External Decline

People commonly perceive social conditions as declining. We propose that perceptions of social decline are often a consequence of a bias whereby people mistake change in themselves for change in the world. The present research demonstrates that common personal changes such as the parenthood transition (Studies 1–2) and physical aging (Study 3) may increase a person's sensitivity to dangers and thereby contribute to an illusory perception that external dangers are increasing. We use experimental models of the hypothesized change processes to test whether these common personal changes may contribute to judgments of social decline.

Early Human Visual Cortex Encodes Surface Brightness Induced by Dynamic Context

Visual scene perception owes greatly to surface features such as color and brightness. Yet, early visual cortical areas predominantly encode surface boundaries rather than surface interiors. Whether human early visual cortex may nevertheless carry a small signal relevant for surface perception is a topic of debate. We induced brightness changes in a physically constant surface by temporally modulating the luminance of surrounding surfaces in seven human participants. We found that fMRI activity in the V2 representation of the constant surface was in antiphase to luminance changes of surrounding surfaces (i.e., activity was in-phase with perceived brightness changes). Moreover, the amplitude of the antiphase fMRI activity in V2 predicted the strength of illusory brightness perception. We interpret our findings as evidence for a surface-related signal in early visual cortex and discuss the neural mechanisms that may underlie that signal in concurrence with its possible interaction with the properties of the fMRI signal.

Free-Energy and Illusions: The Cornsweet Effect

In this paper, we review the nature of illusions using the free-energy formulation of Bayesian perception. We reiterate the notion that illusory percepts are, in fact, Bayes-optimal and represent the most likely explanation for ambiguous sensory input. This point is illustrated using perhaps the simplest of visual illusions; namely, the Cornsweet effect. By using plausible prior beliefs about the spatial gradients of illuminance and reflectance in visual scenes, we show that the Cornsweet effect emerges as a natural consequence of Bayes-optimal perception. Furthermore, we were able to simulate the appearance of secondary illusory percepts (Mach bands) as a function of stimulus contrast. The contrast-dependent emergence of the Cornsweet effect and subsequent appearance of Mach bands were simulated using a simple but plausible generative model. Because our generative model was inverted using a neurobiologically plausible scheme, we could use the inversion as a simulation of neuronal processing and implicit inference. Finally, we were able to verify the qualitative and quantitative predictions of this Bayes-optimal simulation psychophysically, using stimuli presented briefly to normal subjects at different contrast levels, in the context of a fixed alternative forced choice paradigm.

Auditory Time-Interval Perception as Causal Inference on Sound Sources

Perception of a temporal pattern in a sub-second time scale is fundamental to conversation, music perception, and other kinds of sound communication. However, its mechanism is not fully understood. A simple example is hearing three successive sounds with short time intervals. The following misperception of the latter interval is known: underestimation of the latter interval when the former is a little shorter or much longer than the latter, and overestimation of the latter when the former is a little longer or much shorter than the latter. Although this misperception of auditory time intervals for simple stimuli might be a cue to understanding the mechanism of time-interval perception, there exists no model that comprehensively explains it. Considering a previous experiment demonstrating that illusory perception does not occur for stimulus sounds with different frequencies, it might be plausible to think that the underlying mechanism of time-interval perception involves a causal inference on sound sources: herein, different frequencies provide cues for different causes. We construct a Bayesian observer model of this time-interval perception. We introduce a probabilistic variable representing the causality of sounds in the model. As prior knowledge, the observer assumes that a single sound source produces periodic and short time intervals, which is consistent with several previous works. We conducted numerical simulations and confirmed that our model can reproduce the misperception of auditory time intervals. A similar phenomenon has also been reported in visual and tactile modalities, though the time ranges for these are wider. This suggests the existence of a common mechanism for temporal pattern perception over modalities. This is because these different properties can be interpreted as a difference in time resolutions, given that the time resolutions for vision and touch are lower than those for audition.

Directionless Vection: A New Illusory Self-Motion Perception

We report a new visual illusion, “directionless vection.” When expanding and contracting optic flows are simultaneously presented in the same depth plane, observers can perceive illusory self-motion (vection) without direction.