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.     

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).     

Visual angle as a determinant of perceived interobject distance

Two new experiments and a reanalysis of Toye’s (1986)data are used to examine the relationship between true distance and perceived distance in natural scenes. In the first experiment, 8 subjects estimated 78 interobject distances, formed by all pairs of 13 objects, while viewing the objects from a fixed position. The results showed that estimated distance is a linear function of the visual angle between objects as well as of the true distance. This relationship results in distances perpendicular to the line of sight being overestimated in relation to true distances and to distances parallel to the line of sight. These findings were confirmed by reanalysis of a comparable data set from Toye. Since changes in the visual angle can come about through changes in alignment with the line of sight, viewing distance, or interobject distance, Experiment 2 was designed to determine whether the visual angle effect was due to one of these, or whether it was an independent effect. In Experiment 2, 8 subjects estimated six interobject distances from 12 viewing positions. The results showed that visual angle predicted estimated distance independently of how the change in visual angle came about, suggesting that the greater the visual angle between objects, the more their separation is overestimated.     

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.     

Visual size difference discrimination: Effect of disc size and retinal locus

Ability to discriminate between the sizes of two adjacently presented discs of light is considered both as a function of the size of the discs and the retinal locus of their presentation. Ss were required to report whether a comparison disc was seen as larger or the same size as a standard disc when the two were presented briefly together. Results showed that the and required for 50% difference discrimination was independent of the size of the disc and was constant at about 30 sec of arc. For peripheral presentations, the jnd was found to increase in a linear manner with increasing eccentricity of presentation. Comparisons are drawn between the results obtained and peripheral visual acuity data and it is speculated that similar processes are involved in both situations.     

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.     

Gaze cueing as a function of perceived gaze direction

Previous studies have found that attention is automatically oriented in the direction of other people's gaze. This study directly investigated whether the perceiving gaze direction modulates the orienting of observers' attention. Gaze perception was manipulated by changing the face context (head orientation) of the gaze cue: the perceived gaze angle was increased (or decreased) when the head and gaze are congruent (or incongruent), while the local‐feature information of the eye region was preserved for all stimuli. The results showed that gaze‐cueing effects were enhanced when the perceived gaze direction was averted more toward left or right, and reduced when the perceived gaze direction was closer to direct gaze. The results suggest that gaze‐cueing effects are based on mechanisms specialized for gaze perception, and the magnitude of gaze‐cueing effects was probably a function of the perceived gaze direction.