279 research outputs found
The composite illusion requires composite face stimuli to be biologically plausible
AbstractComposite stimuli are whole faces comprised of two halves taken from different individuals. When asked to decide if two identical top halves are the ‘same’, subjects are more accurate (or faster to respond) in misaligned trials, than in aligned trials. This performance advantage for misaligned trials is referred to as the composite face effect (CFE). The proposed explanation is that aligned features are automatically fused together and form a global identity that interferes with the recognition of smaller components (the composite face illusion, CFI). However, when composite faces are misaligned, it appears to be much easier to ignore the identity of the whole face and process individual features. Here we are interested in why misalignment impairs holistic face perception. In Experiment 1 we tested the difference between horizontal and vertical misalignment and found that holistic interference persists when the vertical distance between features is increased. Is this because vertical misalignment leaves features in the correct vertical arrangement, or because vertically stretched faces are biologically plausible? Experiment 2 tested the difference between these two accounts by measuring the CFE when the two halves of a composite face were separated in stereo-depth and demonstrates that vertical symmetry alone is not sufficient for holistic processing. However, when the faces were slanted through stereo-depth (to an equivalent extent), subjects continued to be inaccurate. Overall, these experiments provide strong evidence that the composite illusion depends on biological plausibility in that the faces must be globally coherent
Large shifts in perceived motion direction reveal multiple global motion solutions
AbstractMoving objects are thought to be decomposed into one-dimensional motion components by early cortical visual processing. Two rules describing how these components might be re-combined to produce coherent object motion are the intersection of constraints and the vector average rules. Using stimuli for which these combination rules predict different directional solutions, we found that adapting one of the solutions through motion adaptation switched perceived direction to the other solution. The effects were symmetrical: shifts from IOC to VA, and from VA to IOC, were observed following adaptation. These large shifts indicate that multiple solutions to global motion processing coexist and compete to determine perceived motion direction
Tilt aftereffects and tilt illusions induced by fast translational motion: evidence for motion streaks
Fast-moving visual features are thought to leave neural \u27streaks\u27 that can be detected by orientation-selective cells. Here, we tested whether \u27motion streaks\u27 can induce classic tilt aftereffects (TAEs) and tilt illusions (TIs). For TAEs, participants adapted to random arrays of small Gaussian blobs drifting at 9.5 deg/s. Following adaptation to directions of 15, 30, 45, 60, 75, and 90 degrees (clockwise from vertical) subjective vertical was measured for a briefly presented test grating. For TIs, the same motions were presented in an annular surround and subjective vertical was measured for a simultaneously presented central grating. All motions were 50% coherent, with half the blobs following random-walk paths and half following a fixed direction. Strong and weak streaks were compared by varying streak length (the number of fixed-walk frames), rather than by manipulating speed, so that speed and coherence were matched in all conditions. Strong motion streaks produced robust TAEs and TIs, similar in magnitude and orientation tuning to those induced by tilted lines. These effects were weak or absent in weak streak conditions, and when motion was too slow to form streaks. Together, these results indicate that motion streaks produced by temporal integration of fast translating features do effectively adapt orientation-selective cells and may therefore be exploited to improve perception of motion direction as described in the \u27motion streaks\u27 model
Attraction to the recent past in aesthetic judgments: A positive serial dependence for rating artwork
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Different coding strategies for the perception of stable and changeable facial attributes
Perceptual systems face competing requirements: improving signal-to-noise ratios of noisy images, by integration; and maximising sensitivity to change, by differentiation. Both processes occur in human vision, under different circumstances: they have been termed priming, or serial dependencies, leading to positive sequential effects; and adaptation or habituation, which leads to negative sequential effects. We reasoned that for stable attributes, such as the identity and gender of faces, the system should integrate: while for changeable attributes like facial expression, it should also engage contrast mechanisms to maximise sensitivity to change. Subjects viewed a sequence of images varying simultaneously in gender and expression, and scored each as male or female, and happy or sad. We found strong and consistent positive serial dependencies for gender, and negative dependency for expression, showing that both processes can operate at the same time, on the same stimuli, depending on the attribute being judged. The results point to highly sophisticated mechanisms for optimizing use of past information, either by integration or differentiation, depending on the permanence of that attribute
The ventriloquist effect results from near-optimal bimodal integration
Results for the various unimodal location discriminations for naive observer L.M. are shown in Figure 1A. The curves plot the proportion of trials in which the second stimulus was seen to the left of the first, as a function of actual physical displacement. Following standard practice, the data were fitted with cumulative Gaussian functions free to vary in position and width: the position of the median (50 % leftward) is termed the point of subjective equality (PSE), and the width � 3Department of Psychology represents the estimate of localization accuracy (pre-University of Florence sumed to depend on internal noise). For all unimodal 50125 Florence conditions, the PSE was near 0�, but � varied consider-Italy ably. For visual stimuli, � was smallest (approximatel
Multisensory Congruency as a Mechanism for Attentional Control over Perceptual Selection
The neural mechanisms underlying attentional selection of competing neural signals for awareness remains an unresolved issue. We studied attentional selection, using perceptually ambiguous stimuli in a novel multisensory paradigm that combined competing auditory and competing visual stimuli. We demonstrate that the ability to select, and attentively hold, one of the competing alternatives in either sensory modality is greatly enhanced when there is a matching cross-modal stimulus. Intriguingly, this multimodal enhancement of attentional selection seems to require a conscious act of attention, as passively experiencing the multisensory stimuli did not enhance control over the stimulus. We also demonstrate that congruent auditory or tactile information, and combined auditory–tactile information, aids attentional control over competing visual stimuli and visa versa. Our data suggest a functional role for recently found neurons that combine voluntarily initiated attentional functions across sensory modalities. We argue that these units provide a mechanism for structuring multisensory inputs that are then used to selectively modulate early (unimodal) cortical processing, boosting the gain of task-relevant features for willful control over perceptual awareness
Attentional Modulation of Binocular Rivalry
Ever since Wheatstone initiated the scientific study of binocular rivalry, it has been debated whether the phenomenon is under attentional control. In recent years, the issue of attentional modulation of binocular rivalry has seen a revival. Here we review the classical studies as well as recent advances in the study of attentional modulation of binocular rivalry. We show that (1) voluntary control over binocular rivalry is possible, yet limited, (2) both endogenous and exogenous attention influence perceptual dominance during rivalry, (3) diverting attention from rival displays does not arrest perceptual alternations, and that (4) rival targets by themselves can also attract attention. From a theoretical perspective, we suggest that attention affects binocular rivalry by modulating the effective contrast of the images in competition. This contrast enhancing effect of top-down attention is counteracted by a response attenuating effect of neural adaptation at early levels of visual processing, which weakens the response to the dominant image. Moreover, we conclude that although frontal and parietal brain areas involved in both binocular rivalry and visual attention overlap, an adapting reciprocal inhibition arrangement at early visual cortex is sufficient to trigger switches in perceptual dominance independently of a higher-level “selection” mechanisms. Both of these processes are reciprocal and therefore self-balancing, with the consequence that complete attentional control over binocular rivalry can never be realized
A Collection of Pseudo-Words to Study Multi-Talker Speech Intelligibility without Shifts of Spatial Attention
A new collection of pseudo-words was recorded from a single female speaker of American English for use in multi-talker speech intelligibility research. The pseudo-words (known as the KARG collection) consist of three groups of single syllable pseudo-words varying only by the initial phoneme. The KARG method allows speech intelligibility to be studied free of the influence of shifts of spatial attention from one loudspeaker location to another in multi-talker contexts. To achieve this, all KARG pseudo-words share the same concluding rimes, with only the first phoneme serving as a distinguishing identifier. This ensures that listeners are unable to correctly identify the target pseudo-word without hearing the initial phoneme. As the duration of all the initial phonemes are brief, much shorter than the time required to spatially shift attention, the KARG method assesses speech intelligibility without the confound of shifting spatial attention. The KARG collection is available free for research purposes
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