Seeing and Perceiving最新文献

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 participants' task was to observe the quasi-naturalistic stimulus sequences and to perform a standard classification. The addition of stimuli of the second modality indeed facilitated apparent motion perception. Bimodal presentation increased the upper temporal interval up to which the stimuli could be separated in time while still being perceived as continuous motion. We interpret these results as evidence for an ecologically advantageous audiovisual motion integration mechanism which operates beyond the constraints of strict spatiotemporal coincidence. Functional considerations suggest that this mechanism may represent an amodal stage suited for the processing of both unimodal and bimodal signals.

This study tests the hypothesis that patients with bilateral glaucoma exhibit different eye movements compared to normally-sighted people when viewing computer displayed photographs of everyday scenes. Thirty glaucomatous patients and 30 age-related controls with normal vision viewed images on a computer monitor whilst eye movements were simultaneously recorded using an eye tracking system. The patients demonstrated a significant reduction in the average number of saccades compared to controls (P = 0.02; mean reduction of 7% (95% confidence interval (CI): 3-11%)). There was no difference in average saccade amplitude between groups but there was between-person variability in patients. The average elliptical region scanned by the patients by a bivariate contour ellipse area (BCEA) analysis, was more restricted compared to controls (P = 0.004; mean reduction of 23% (95% (CI): 11-35%)). A novel analysis mapping areas of interest in the images indicated a weak association between severity of functional deficit and a tendency to not view regions typically viewed by the controls. In conclusion, some eye movements in some patients with bilateral glaucomatous defects differ from normal-sighted people of a similar age when viewing images of everyday scenes, providing evidence for a potential new window for looking into the functional consequences of the disease.

It is a well-known fact that the perceived brightness of any surface depends on the brightness of the surfaces that surround it. This phenomenon is termed as brightness induction. Isotropic arrays of multi-scale DoG (Difference of Gaussians) as well as cortical Oriented DoG (ODOG) and extensions thereof, like the Frequency-specific Locally Normalized ODOG (FLODOG) functions have been employed towards prediction of the direction of brightness induction in many brightness perception effects. But the neural basis of such spatial filters is seldom obvious. For instance, the visual information from retinal ganglion cells to such spatial filters, which have been generally speculated to appear at the early stage of cortical processing, are fed by at least three parallel channels viz. Parvocellular (P), Magnocellular (M) and Koniocellular (K) in the subcortical pathway, but the role of such pathways in brightness induction is generally not implicit. In this work, three different spatial filters based on an extended classical receptive field (ECRF) model of retinal ganglion cells, have been approximately related to the spatial contrast sensitivity functions of these three parallel channels. Based on our analysis involving different brightness perception effects, we propose that the M channel, with maximum conduction velocity, may have a special role for an initial sensorial perception. As a result, brightness assimilation may be the consequence of vision at a glance through the M pathway; contrast effect may be the consequence of a subsequent vision with scrutiny through the P channel; and the K pathway response may represent an intermediate situation resulting in ambiguity in brightness perception. The present work attempts to correlate this phenomenon of pathway selection with the complementary nature of these channels in terms of spatial frequency as well as contrast.

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. To simulate monovision correction with +1.5 or +2.5 D defocus, the images of the line patterns presented to one eye were spatially low-pass filtered while the patterns presented to the other eye remained unfiltered.

Results: Compared to binocular viewing without blur, Dmin is elevated substantially more in the presence of monocular than binocular simulated blur. Dmax is reduced in the presence of simulated monocular blur by between 13 and 44%, compared to when the images in both eyes are clear. In contrast, when the targets presented to both eyes are blurred equally, Dmax either is unchanged or increases slightly, compared to the values measured with no blur.

Conclusion: In conjunction with the elevation of Dmin, the reduction of Dmax with monocular blur indicates that the range of useful stereoscopic depth perception is likely to be compressed in patients who wear monovision corrections.