Seeing and Perceiving

Several definitions, measurements, and implicit meanings of 'fixation stability' have been used in clinical vision research, leading to some confusion. One definition concerns eye movements observed within fixations (i.e., within periods separated by saccades) when observing a point target: drift, microsaccades and physiological tremor all lead to some degree of within-fixation instability. A second definition relates to eye position during multiple fixations (and saccades) when patients fixate a point target...

For low vision navigation, misperceiving the locations of hazards can have serious consequences. Potential sources of such misperceptions are hazards that are not visually associated with the ground plane, thus, depriving the viewer of important perspective cues for egocentric distance. In Experiment 1, we assessed absolute distance and size judgments to targets on stands under degraded vision conditions. Normally sighted observers wore blur goggles that severely reduced acuity and contrast, and viewed targets placed on either detectable or undetectable stands...

Visually induced illusions of self-motion (vection) are often induced using constant velocity optic flow. However, adding simulated viewpoint jitter and oscillation to these displayscan significantly improve the vection experience (especially when this jitter/oscillation is orthogonal to the constant flow component - Nakamura, 2010; Palmisano et al., 2008). In the present experiment, we found that vection was only facilitated when luminance-, but not contrast-, defined vertical oscillatory motion was added to the constant horizontal display motion (even though observers clearly reported seeing both the oscillatory and constant display motions in both conditions)...

Audiovisual speech perception is an everyday occurrence of multisensory integration. Conflicting visual speech information can influence the perception of acoustic speech (namely the McGurk effect), and auditory and visual speech are integrated over a rather wide range of temporal offsets. This research examined whether the addition of a concurrent cognitive load task would affect the audiovisual integration in a McGurk speech task and whether the cognitive load task would cause more interference at increasing offsets...

The phenomenon of crossmodal dynamic visual capture occurs when the direction of motion of a visual cue causes a weakening or reversal of the perceived direction of motion of a concurrently presented auditory stimulus. It is known that there is a perceptual bias towards looming compared to receding stimuli, and faster bimodal reaction times have recently been observed for looming cues compared to receding cues (Cappe et al., 2009). The current studies aimed to test whether visual looming cues are associated with greater dynamic capture of auditory motion in depth compared to receding signals...

We investigated audiovisual interactions in motion perception by behavioral experiments testing both, the influence of visual stimuli on auditory apparent motion and the influence of auditory stimuli on visual apparent motion perception. A set of loudspeakers with an LED mounted in the middle of each speaker cone was arranged in a semicircle. Apparent motion streams were presented for each modality alone in the unimodal conditions. In the bimodal conditions, stimuli of the second modality were added to fill the temporal and spatial gaps of the sampled trajectory of the reference stream...

The fulcrum principle establishes that a subthreshold excitatory signal (entering in one sense) that is synchronous with a facilitation signal (entering in a different sense) can be increased (up to a resonant-like level) and then decreased by the energy and frequency content of the facilitating signal. As a result, the sensation of the signal changes according to the excitatory signal strength. In this context, the sensitivity transitions represent the change from subthreshold activity to a firing activity in multisensory neurons...

Biological motion is usually associated with highly correlated sensory signals from more than one modality: an approaching human walker will not only have a visual representation, namely an increase in the retinal size of the walker's image, but also a synchronous auditory signal since the walker's footsteps will grow louder. We investigated whether the multisensorial processing of biological motion is subject to different constraints than ecologically invalid motion. Observers were presented with a visual point-light walker and/or synchronised auditory footsteps; the walker was either approaching the observer (looming motion) or walking away (receding motion)...

Exposure to synchronous but spatially discordant auditory and visual inputs produces adaptive recalibration of the respective localization processes, which manifest themselves in measurable aftereffects. Here we report two experiments that examined the time course of visual recalibration of apparent sound location in order to establish the build-up and dissipation of recalibration. In Experiment 1 participants performed a sound localization task before and during exposure to an auditory-visual discrepancy. In Experiment 2, participants performed a sound localization task before and after 60, 180 or 300 exposures to the discrepancy and aftereffects were measured across a series of post-adaptation sound localization trials...

Human observers adjust the frontal view of a wireframe box on a computer screen so as to look equally deep and wide, so that in the intended setting the box looks like a cube. Perspective cues are limited to the size-distance effect, since all angles are fixed. Both the size on the screen, and the viewing distance from the observer to the screen were varied. All observers prefer a template view of a cube over a veridical rendering, independent of picture size and viewing distance. If the rendering shows greater or lesser foreshortening than the template, the box appears like a long corridor or a shallow slab, that is, like a 'deformed' cube...

Perceptual analogues of centre-surround suppression have been applied as indirect measures of cortical inhibitory function in several clinical disorders. Two tasks have been used: a centre-surround contrast perception task and a motion direction discrimination task, where the stimulus size and contrast is varied to measure surround suppression effects. The tasks are markedly different, yet previous literature implies that both measures indirectly assess inhibitory function and that results will be complementary...

Shape from shading arose from artistic practice, and later experimental psychology, but its formal structure has only been established recently by computer vision. Some of its algorithms have led to useful applications. Psychology has reversely borrowed these formalisms in attempts to come to grips with shading as a depth cue. Results have been less than spectacular. The reason might well be that these formalisms are all based on Euclidean geometry and physics (radiometry), which, are the right tools in third person accounts, but have little relevance to first person accounts, and thus are biologically (and consequently psychologically) of minor interest...

Numerous studies have demonstrated that sighted and blind individuals find it difficult to recognize tactile pictures of common objects. However, it is still not clear what makes recognition of tactile pictures so difficult. One possibility is that observers have difficulty acquiring the global shape of the image when feeling it. Alternatively, observers may have an accurate understanding of the shape but are unable to link it to a particular object representation. We, therefore, conducted two experiments to determine where tactile picture recognition goes awry...

PURPOSE: Persons who wear monovision correction typically receive a clear image in one eye and a blurred image in the other eye. Although monovision is known to elevate the minimum stereoscopic threshold (Dmin), it is uncertain how it influences the largest binocular disparity for which the direction of depth can reliably be perceived (Dmax). In this study, we compared Dmax for stereo when one eye's image is blurred to Dmax when both eyes' images are either clear or blurred. METHODS: The stimulus was a pair of vertically oriented, random-line patterns...

We studied how stimulus attributes (angle polarity and perspective) and data-driven signals (motion parallax and binocular disparity) affect recovery of 3-D shape. We used physical stimuli, which consisted of two congruent trapezoids forming a dihedral angle. To study the effects of the stimulus attributes, we used 2 × 2 combinations of convex/concave angles and proper/reverse perspective cues. To study the effects of binocular disparity and motion parallax, we used 2 × 2 combinations of monocular/binocular viewing with moving/stationary observers...

Rules and similarity are at the heart of our understanding of human categorization. However, it is difficult to distinguish their role as both determinants of categorization are confounded in many real situations. Rules are based on a number of identical properties between objects but these correspondences also make objects appearing more similar. Here, we introduced a stimulus set where rules and similarity were unconfounded and we let participants generalize category examples towards new instances. We also introduced a method based on the frequency distribution of the formed partitions in the stimulus sets, which allowed us to verify the role of rules and similarity in categorization...

We examined the crossmodal effect of the presentation of a simultaneous sound on visual detection and discrimination sensitivity using the equivalent noise paradigm (Dosher and Lu, 1998). In each trial, a tilted Gabor patch was presented in either the first or second of two intervals embedded in dynamic 2D white noise with one of seven possible contrast levels. The results revealed that the sensitivity of participants' visual detection and discrimination performance were both enhanced by the presentation of a simultaneous sound, though only close to the noise level at which participants' target contrast thresholds started to increase with the increasing noise contrast...

The aim of this work is to demonstrate a new principle of grouping and shape formation that we called the accentuation principle, stating that, all else being equal, the elements tend to group in the same oriented direction of the element discontinuity placed within a whole set of continuous/homogeneous components. The discontinuous element is like an accent, i.e., a visual emphasis within a whole. We showed that this principle is independent from other gestalt principles. In fact, it shows vectorial properties not present in the other principles...

A large proportion of the human cortex is devoted to visual processing. Contrary to the traditional belief that multimodal integration takes place in multimodal processing areas separate from visual cortex, several studies have found that sounds may directly alter processing in visual brain areas. Furthermore, recent findings show that perceptual learning can change the perceptual mechanisms that relate auditory and visual senses. However, there is still a debate about the systems involved in cross-modal learning...

In Illusory Flash (IF) experiments, congruent multisensory presentation has no effect on the mean estimate of the number of events, but decreases the variance in comparison with unisensory presentation. In contrast, congruent multisensory presentation in other Temporal Numerosity Judgement (TNJ) tasks affects the mean estimate (i.e., it often results in a reduction in underestimation) and increases the variance. In three experiments, we investigated the differences between both paradigms as possible causes of this discrepancy: the presence or absence of incongruent stimuli (Experiment 1), the instruction to the observer to either count flashes, beeps or multisensory events (Experiment 2), and the range of pulses presented (Experiment 3)...