Search PubMed⌕ Search
Home/Archive/PubMed

PubMed · 7922357

Visual perception. Knowing is seeing.

A C Hurlbert
View original source ↗Export metadata ↓

Abstract

New visual illusions provide further evidence for the influence of higher-order analyses of the visual scene on the perceived brightnesses of surfaces within that scene.

Explore related subjects

Contrast SensitivityHumansLightModels, PsychologicalOptical IllusionsVisual PerceptionJournal ArticleReview

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

A C Hurlbert. 1994-05-01. Visual perception. Knowing is seeing.. https://doi.org/10.1016/s0960-9822(00)00092-0

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed1996

Perception of motion smear in normal observers and in persons with congenital nystagmus.

PURPOSE: Despite incessant motion of the retinal image, persons with congenital nystagmus (CN) usually do not report that targets are smeared. The authors investigated whether the brief stationary glimpses of a target that occur during foveation periods in the CN waveform contribute to the alleviation of perceived smear. METHODS: Retinal image motion simulating that in jerk nystagmus was produced in normal observers (N = 10) who monocularly viewed either a 5-minute or a 1 degree luminous disk reflected from a horizontally oscillating mirror. Contrast sensitivities to detect each target and to perceive the presence of motion smear were determined for two simulated CN waveforms; observers also estimated the length and brightness of perceived smear for several suprathreshold target luminances. One waveform was a 7 degrees, 4-Hz ramp that included 120 msec zero-velocity intervals, simulating the foveation periods in the CN waveform. The second waveform lacked the zero-velocity simulated foveation periods. For comparison, estimates of perceived smear for physically stationary targets were obtained from three observers with CN. RESULTS: Normal observers' contrast sensitivities for perceiving smear were nearly identical for the simulated CN waveforms with and without a 120-msec foveation period. Estimated length and brightness of perceived smear for suprathreshold targets increased similarly with luminance for both waveforms. Observers with CN reported substantially less smear than did normal observers. CONCLUSIONS: Glimpses of a stationary retinal image during simulated foveation periods do not attenuate the perception of motion-induced smear in normal observers. In persons with CN, the perception of smear may be reduced by the extraretinal signals that accompany their eye movements.

Contrast Sensitivity↗
PubMed1995

Blindsight in normal observers.

Some patients with lesions in visual cortex lack conscious visual experience but, when tested, exhibit a significant ability, termed 'blindsight', to discriminate visual stimuli. Here we report two different visual displays that induce blindsight in normal observers. Using an objective measure, we show that conscious experience remains defective at presentation times much longer (1 s) than the onset of visual sensitivity (approximately 60 ms). To obtain this effect, we generate a contrast between visual textures and then conceal the contrast by superimposing 'complementary' textures. Complementarity can involve either opposite motion or binocular rivalry and orthogonal orientation. In both cases, observers locate the texture contrast reliably but do not, by either subjective or objective measures, consciously experience it. Taken together with present knowledge of the visual cortical site(s) at which opposite motion and rivalrous orientation interact, this observation bears upon the functional anatomy of conscious visual experience.

Contrast Sensitivity↗
PubMed1995

Two stages of visual processing for radial and circular motion.

As we move through our environment, the flow of the deforming images on our retinae provides rich information about ego motion and about the three-dimensional structure of the external world. Flow-fields comprise five independent components, including radial and circular motion. Here we provide psychophysical evidence for the existence of neural mechanisms in human vision that integrate motion signals along these complex trajectories. Signal-to-noise sensitivity for discriminating the direction of radial, circular and translational motion increased predictably with the number of exposed sectors, implying the existence of specialized detectors that integrate motion signals of different directions from different locations. However, contrast sensitivity for complex motion did not increase greatly with sector number, implying that the specialized detectors are preceded by a first stage of local-motion mechanisms that impose a contrast threshold. These findings fit well with recent electrophysiological evidence in monkey showing that whereas motion-sensitive neurons in primary visual cortex respond best to local translation, many neurons in the medial superior temporal cortex have large receptive fields tuned to radial, circular or spiral motion.

Contrast Sensitivity↗