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Biomedical subjects

V F Emerson

Publications and source records attributed to V F Emerson.

12 recordsLinked to original sources
PubMed1989

Pattern-contingent color aftereffects on noninduced patterns.

In a series of experiments, we found that in addition to expected reports of color aftereffects on patterns viewed during induction, reliable and predictable reports of color were given by subjects to patterns they did not view during induction. These reports to noninduced patterns were generally to patterns that were orthogonal to the patterns seen during induction. Induction with, for example, a red vertical grating led to appropriate aftereffects (i.e., green) on that vertical pattern and to the complementary aftereffect (i.e., pink) on a horizontal grating. We suggest that such color aftereffects on noninduced patterns are based on a shift in the activity of orientation coding mechanisms as a result of viewing the inducing patterns. We further propose that the results are consistent with the Lie transformation group theory of neuropsychology and that they add to a growing body of research demonstrating the applicability of this theory to the understanding of pattern-contingent color aftereffects.

Attention↗
PubMed1983

Grating acuity of the Mongolian gerbil (Meriones unguiculatus).

The grating acuity of the Mongolian gerbil was measured using a two-alternative forced-choice task in a jumping stand. Frequency-of-seeing curves generated by a modified method of limits indicated that the acuity of the gerbil for a horizontal square-wave grating is about 1.5-2.0 cycles/degree (c/deg) at 70 cd/m2, using the 70%- and 80%-correct levels of performance as criteria for defining acuity. The acuity for horizontal gratings is reliably better than that for vertical gratings, and this difference does not appear to be luminance-dependent. A corresponding orientation anisotropy is not seen in acquisition scores, nor is an 'oblique effect' evident. The acuity of the gerbil continues to increase with luminance into the (human) photopic range, suggesting the existence of a functional cone system. The gerbil visual system appears to be well adapted for detail vision in a diurnal lifestyle.

Animals↗
PubMed1982

Behavioural, physiological, and anatomical consequences of monocular deprivation in the golden hamster (Mesocricetus auratus).

The effects of long-term monocular deprivation (MD) on the visual acuity, cortical physiology and dLGN anatomy of the golden hamster were assessed in adult animals which had undergone unilateral eyelid suture at the time of natural eyelid opening. Acuity was measured in a two-alternative forced-choice task in a Y-maze, using a modified method of constant stimuli to vary the spatial frequency of a high-contrast square-wave grating which had the same mean luminance (5 cd/m2) as a uniform grey card. The acuity of the normal (non-deprived) eye of each of two early-MD hamsters was within the normal range (about 0.5 cycles per degree of visual angle), but the acuity of the deprived eyes was reduced by about 0.6 octaves at the 70%-correct criterion. A second reversal of eyelid suture and retesting through the "normal" eye demonstrated that this acuity difference was not attributable to surgical artifacts. Another hamster undergoing prolonged MD beginning in adulthood had normal acuity in both eyes, indicating a "sensitive period" in the development of the hamster's visual system. Single-unit recording from area V1 of the cortex of four early-MD hamsters revealed a shift in ocular dominance favouring the normal eye. The deprived eye's loss of excitatory influence was greater in the ipsilateral hemisphere, but even here 57% of cells were binocularly driven. Only small differences were observed in other receptive field properties. In the dLGN, cell areas in the deprived "lamina" were about 4% smaller than in the non-deprived areas after 5-7.5 months of MD, a difference which was statistically non-significant. However, this difference increased to 19.5% in one hamster in which MD lasted 17 months (p less than 0.025). The relatively small MD effect observed in the hamster is interpreted as being consistent with the absence of a sensitive "detail-analysing" mechanism in the hamster's visual system.

Animals↗
PubMed1980

Grating acuity of the golden hamster. The effects of stimulus orientation and luminance.

Twelve golden hamsters learned visual discriminations in a Y-maze for a food reward. After initial training on a light/dark task, the hamsters learned to discriminate a grating from a uniform grey field of the same mean luminance as the grating; grating orientation was varied among hamsters. Those animals trained with the grating vertical or horizontal learned significantly faster than those trained on obliques. Acuity, measured by varying the spatial frequency of the grating according to the descending method of limits or the method of constant stimuli, was determined to be about 0.7 c/deg at 50% correct or 0.5 c/deg at 70% correct for all orientations tested (0 degrees, 45 degrees, 90 degrees, 135 degrees). Acuity was relatively constant within the human photopic range, but decreased to about 0.35 c/deg at 5 x 10(-4)cd/m2. The change in acuity as a function of luminance suggests that the hamster has a rod-dominated retina.

Animals↗
PubMed1977

Measurement of visual preferences in cats.

A technique is described for measuring visual preferences in cats. The method involves a self-presentation paradigm, but provides strict control of the visual field and orientation of contours in the field. Two procedures are presented: a single-choice design and a multiple-choice design, both of which use duration of self-produced exposure as the dependent measure. Although both procedures may serve as indices of preference order, the multiple-choice method is preferable for measuring preference strength. The application of the technique as a behaviorual index of the effects of early environmental manipulation is suggested. Preliminary data from two normal cats indicate that, although homogeneous illumination is reinforcing, the presence of features, especially oriented contours, appears to increase the 'interest' value of the presentation.

Animals↗
PubMed1972

Motion perception: a color-contingent aftereffect.

When observers who watched repeated alternations of a red contracting spiral and green expanding spiral were later shown stationary spirals, red and a green the red stationary spiral appeared to be expanding and the green stationary spiral appeared to be contracting. These color-contingent motion after effects complement reports of motion-contingent color aftereffects and suggest that both may reflect adaptation of detectors specific to color and motion.

Adolescent↗