Brightness as a function of retinal locus

Brightness functions were determined for the dark-adapted fovea and periphery. In one series of experiments, observers matched numbers to the brightness of a 1° white target at various intensities, presented half the time to the fovea, the other half to one of five peripheral loci: 5°, 12°, 20°, 35°, and 60°. In a second series, observers matched the brightness of a 1° white target in the fovea of one eye to the brightness of an identical target in the periphery of the other eye at various intensities. Thresholds were also determined for the fovea and for the five peripheral loci by a staircase procedure. The magnitude estimations and the interocular matches concur in showing that a stimulus of fixed luminance appears brighter in the periphery than in the fovea. The brightness was found to be maximal at 20°. Brightness grows as a similar power function of luminance at all six retinal positions.     

Border contrast as a function of retinal locus

When the visibility of a small test spot was measured by direct brightness matching at various locations along the white edge of a black and white border, it was found that the white background was perceived as becoming progessively brighter as the border was approached. The effect was greater when a corner was neared. Moreover, greater effects, i.e., larger differences between the edge effect and base level (no border) were found at distances farther removed from the fovea (0 deg 12 min to 3 deg 52 min).     

Brightness exponent as a function of flash duration and retinal eccentricity

The effect of flash duration on the exponent of the brightness power function was investigated in the fovea and 20-deg periphery using a method of direct magnitude estimation. The flash duration employed covered a 5-log-unit range between .001 and 100 sec. The results showed that the exponent is clearly time-dependent for both extremes of the duration—that is, very short (.001 to .1 sec) and prolonged (3 to 100 sec) durations—but not for the medium flash durations between .1 and 3 sec. Furthermore, the exponent is a little larger for peripheral viewing than for foveal viewing except for the durations below approximately .03 sec. The systematic change of the exponent as a function of duration is discussed in terms of retinal and postretinal intensity coding functions.     

Brightness and retinal locus: Effects of target size and spectral composition

Ss gave numerical estimates of brightness for stimuli presented to the foveal and peripheral retina. Experiment 1 showed that the periphery’s superior sensitivity to white light is relatively independent of target size. Experiment 2 showed that the periphery is more sensitive than the fovea to violet light, but is less sensitive than the fovea to red light. These results are explicable in terms of differences between rod and cone mediation of brightness.     

Visual beats: Preliminary observations of perceived rate as a function of retinal locus stimulated

Visual beats produced by simultaneous presentation of two different flicker frequencies were used to determine the temporal processing of various retinal areas. The dichoptic presentation of two different flicker frequencies to the center and periphery of the retina resulted in a perceived beat rate that equalled the physical beat frequency. When the stimuli were presented to more discrete retinal areas (temporal vs temporal and nasal vs temporal), the perceived beat rate also equalled the physical beat frequency. The data indicate that different flicker frequencies stimulating divergent retinal loei can be represented accurately and simultaneously in the visual system: Differences in temporal resolution at the different retinal loei do not occur for this repetitive stimulation.     

Duration of the motion aftereffect as a function of retinal locus and visual field.

The duration of the aftereffect induced by viewing a rotating disc was recorded separately for the four hemiretinae of the left and right eyes using a new method of measurement. The results showed duration of aftereffect to differ between nasal and temporal hemiretinae of the right eye and between left and right cerebral hemispheres.     

Brightness exponent as a function of retinal eccentricity in the peripheral visual field: Effects of dark and light adaptation

Using a method of direct magnitude estimation, the exponent of the brightness power function was determined under dark and light adaptation at luminance levels well above threshold. The exponent was estimated for functions describing the brightness of stimuli presented at the fovea and the following peripheral retinal loci: 10, 20, 30, 40, and 50 deg nasally eccentric to the fovea along the horizontal meridian of the right eye. The exponent for a 1-sec flash was found to be approximately .33 at the fovea and increased slightly with increasing retinal eccentricity.The effect of adaptation on the brightness exponent was not so large when the target luminance was set well above threshold.     

Perceived roughness as a function of body locus

Twenty subjects made magnitude estimates of the roughness of grooved metallic surfaces applied to 10 body loci. To a first approximation, perceived roughness grew as a power function of groove width, in accordance with earlier studies. The exponents and intercepts (up-down position in log-log coordinates) of the power function turn out to depend strongly on body locus. The straight lines in log-log coordinates tend to diverge with groove width so that differences among body loci are especially pronounced at large groove widths. Sensitivity to roughness was greatest for the lips, fingers, and forearm, and least for the heel, back, and thigh. The rank order of the body loci in terms of roughness sensitivity closely parallels the rank order for punctate pressure sensitivity, as reported by von Frey in 1894, but apparently not for other measures of tactile sensitivity, such as vibration thresholds to various frequencies, two-point thresholds, and error of point localization.     

Retroactive inhibition as a function of the locus of categorized response sets

The effects which list-level taxonomic attributes should have upon retroactive inhibition (RI) producing mechanisms in both response-set interference theory (Postman & Stark, 1969) and Petrich’s (1975) retrieval model are discussed. A test of the theories was performed by manipulating the presence (1) or absence (0) of categorized response sets in both original learning (OL) and interpolated learning IIL), and comparing their predictions concerning the relative degree of RI expected in the four conditions (0-0, 0-1, 1-0, 1-1). In line with Petrich’s predictions, OL categorization significantly reduced RI, IL categorization significantly increased RI, and 0-1 produced significantly greater RI than 1-0. Moreover, the obtained ranking of the means for the experimental groups in degree of RI (0–1>0-0>1-0 ? 1-1) was in close agreement with the ranking predicted by Petrich’s (1975) model. The results provide support for Petrich’s (1975) retrieval model and pose explanatory problems for response-set interference theory (Postman & Stark, 1969).