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Biomedical subjects

R Blake

Publications and source records attributed to R Blake.

At least 145 records · Page 8Linked to original sources
PubMed1981

Interocular transfer of visual aftereffects.

A number of the well-known visual after-effects of adaptation exhibit interocular transfer, so that presentation of an adaptation figure to one eye produces a temporary change in the performance of the nonadapted eye. This outcome is usually attributed to the involvement of binocular visual neurons that respond to stimulation of either eye. The fact that interocular transfer is incomplete (i.e., the transferred aftereffect is smaller in magnitude than that induced and measured in the same eye) is routinely cited as evidence for the involvement of monocular neurons. This article critically examines these two interpretations, which are developed in terms of a neural model of interocular transfer. No evidence, logical or empirical, was obtained for rejecting the model. Our analysis further shows that the model must assume some type of pooling process that operates over all tested neurons, both adapted and unadapted. Finally, general implications of the interocular transfer model are discussed, the aim being to delimit the conclusions that may be drawn from interocular transfer experiments.

Adaptation, Ocular↗
PubMed1981

Critical bands in cat spatial vision.

1. The ability of cats to detect sinusoidal grating patterns superimposed on one-dimensional visual noise was assessed using behavioural methods. 2. The magnitude of elevation in contrast threshold due to noise increased monotonically within limits with increasing noise contrast. 3. Visual noise was filtered using various techniques (band-reject, low-pass, high-pass and band-pass noise); filtered noise resulted in threshold elevation only when it contained frequencies similar to the test frequency. 4. In all cases the masking functions indicated that the band widths of the channels mediating detection ranged from +/- 0.50 to +/- 0.75 octaves across three spatial frequencies and that the channel sensitive to low spatial frequencies was asymmetrical in its tuning. 5. The spatial properties of these psychophysical detecting channels closely resemble the spatial frequency selectivity exhibited by some cat cortical neurones, both in the general narrowness of tuning and the asymmetry in tuning at lower, but not higher, spatial frequencies.

Animals↗
PubMed1980

Do the two eyes constitute separate visual channels?

A two-interval forced-choice procedure was used to study monocular detection of a briefly presented low-contrast sine-wave grating pattern. Uncertainty about which eye was stimulated degraded detection performance for stereo-blind observers but not for normal ones. These results relate to selective monocular suppression, stereopsis, and other forms of binocular interaction and suggest the level at which inputs to the two eyes are combined neurally.

Form Perception↗
PubMed1980

Temporal properties of binocular mechanisms in the human visual system.

A dichoptic stimulation paradigm was used to determine the degree to which the two monocular images must match in terms of the temporal properties to yield facilitation in binocular grating detection. Several converging lines of evidence point to the existence of two separate neural mechanisms in binocular detection. One of these mechanisms is selective for temporal frequency and limited in its capacity to integrate information from the two eyes over time. The other mechanism is much less selective for temporal frequency and integrates over a longer period of time. At threshold these two separate mechanisms behave independently and exhibit similar degrees of binocular summation.

Flicker Fusion↗
PubMed1980

What is suppressed during binocular rivalry?

To answer the question 'what is suppressed during binocular rivalry?" a series of three experiments was performed. In the first experiment observers viewed binocular rivalry between orthogonally oriented patterns. When the dominant and suppressed patterns were interchanged between the eyes observers continued seeing with the dominant eye, indicating that an eye, not a pattern, is suppressed during rivalry. In a second experiment it was found that a suppressed eye was able to contribute to stereopsis. A third experiment demonstrated that the predominance of an eye could be influenced by prior adaptation of the other eye, indicating that binocular mechanisms participate in the rivalry process.

Adaptation, Ocular↗
PubMed1980

Reaction time as a measure of binocular interaction in human vision.

In a series of psychophysical experiments monocular and binocular reaction times (RTs) were measured in response to the presentation of sinusoidal grating patterns. Over a wide range of contrast values, binocular RT was consistently faster than monocular RT, even at high-contrast levels where RT had reached asymptotic levels. For observers with good stereopsis this binocular summation effect was greater than that expected on the basis of probability summation alone, whereas observers with deficient stereopsis performed at the level of probability summation. For normal observers broadband random noise presented to one eye produced an elevation in RT to gratings presented to the other eye; no such dichoptic masking effect was found in a stereoblind observer. These results validate the use of RT as an efficient, reliable measure of binocular interaction in human vision.

Amblyopia↗
PubMed1979

Psychophysical evidence for a monocular visual cortex in stereoblind humans.

Human observers who lack stereopsis reliably make eye-of-origin discriminations for grating patterns under conditions that render the performance of normal observers unreliable. This lends support to the view that stereoblind individuals possess proportions of monocular and binocular cortical cells similar to those of cats and monkeys deprived of early binocular visual experience.

Depth Perception↗
PubMed1979

On the inhibitory nature of binocular rivalry suppression.

During binocular rivalry the average duration of a suppression phase depends on the stimulus strength (e.g., contrast) of the input to the suppressed eye. To determine if a similar relationship exists between stimulus strength and the inhibitory effect of suppression on test probe detectability, a series of experiments was performed. Using two-alternative forced-choice procedures, increment detection thresholds were measured during phases of dominance and suppression. Results from three trained observers show that detection performance is significantly impaired during suppression by an amount that is independent of any difference in contrast between the rivalrous stimuli. These data indicate that the magnitude of the inhibitory effect of suppression is governed by a mechanism other than that which determines suppression duration.

Adult↗
PubMed1979

The site of binocular rivalry suppression.

Two experiments were performed to localize the site of binocular rivalry suppression in relation to the locus of grating adaptation. In one experiment it was found that phenomenal suppression of a high-contrast adaptation grating presented to one eye had no influence on the strength of the threshold-elevation aftereffect measured interocularly. Evidently information about the adaptation grating arrives at the site of the aftereffect (presumably binocular neurons) even during suppression. In a second experiment 60 s of grating adaptation was found to produce a short-term reduction in the predominance of the adapted eye during binocular rivalry. These findings provide converging lines of evidence that suppression occurs at a site in the human visual system after the locus of grating adaptation and, hence, after the striate cortex.

Adaptation, Ocular↗