Light and dark adaptation of visually perceived eye level controlled by visual pitch

The pitch of a visual field systematically influences the elevation at which a monocularly viewing subject sets a target so as to appear at visually perceived eye level (VPEL). The deviation of the setting from true eye level averages approximately 0.6 times the angle of pitch while viewing a fully illuminated complexly structured visual field and is only slightly less with one or two pitched-from-vertical lines in a dark field (Matin & Li, 1994a). The deviation of VPEL from baseline following 20 min of dark adaptation reaches its full value less than 1 min after the onset of illumination of the pitched visual field and decays exponentially in darkness following 5 min of exposure to visual pitch, either 30° topbackward or 20° topforward. The magnitude of the VPEL deviation measured with the dark-adapted right eye following left-eye exposure to pitch was 85% of the deviation that followed pitch exposure of the right eye itself. Time constants for VPEL decay to the dark baseline were the same for same-eye and cross-adaptation conditions and averaged about 4 min. The time constants for decay during dark adaptation were somewhat smaller, and the change during dark adaptation extended over a 16% smaller range following the viewing of the dim two-line pitched-from-vertical stimulus than following the viewing of the complex field. The temporal course of light and dark adaptation of VPEL is virtually identical to the course of light and dark adaptation of the scotopic luminance threshold following exposure to the same luminance. We suggest that, following rod stimulation along particular retinal orientations by portions of the pitched visual field, the storage of the adaptation process resides in the retinogeniculate system and is manifested in the focal system as a change in luminance threshold and in the ambient system as a change in VPEL. The linear model previously developed to account for VPEL, which was based on the interaction of influences from the pitched visual field and extraretinal influences from the body-referenced mechanism, was employed to incorporate the effects of adaptation. Connections between VPEL adaptation and other cases of perceptual adaptation of visual direction are described.     

Spatial layout, orientation relative to the observer, and perceived projection in pictures viewed at an angle

Judgments of the spatial layout of a three-dimensional array of pictured dowels remain relatively constant as viewing angle changes, whereas judgments of their orientation relative to the observer (perceived orientation) vary. These changes in perceived orientation as viewing angle changes, called the differential rotation effect (DRE), also occur for stimuli such as the eyes in portraits, which are not extended in pictorial space. Thus, the mechanism for the DRE does not depend on the extension of pictured objects in depth. The DRE is decreased when back-illuminated pictures are viewed in the dark so that the picture plane is not visible. This result suggests that the DRE depends on information that defines a pictured object's direction relative to the picture plane. The difference in the way spatial layout and perceived orientation are affected by changes in viewing angle suggests that it is important to distinguish between these two attributes of pictures. In addition, another attribute, the picture's projection, should be distinguished from spatial layout and perceived orientation. When these distinctions are not made, the result is confusion, particularly when discussing whether or not pictures viewed at an angle appear distorted.     

Achromatic surface color and the direction of illumination

Hochberg and Beck (1954) found that an objectively upright trapezoid, when illuminated from above, appeared darker if it was viewed monocularly and lighter if it was viewed binocularly. Illuminated from in front, the same trapezoid then appeared lighter under monocular and darker under binocular viewing. Since the target appeared slanted under monocular but upright under binocular viewing, these changes in apparent lightness could be attributed, wholly or in part, to the apparent angle of incidence of the illumination on the surface. In two experiments, when 8-min periods of dark adaptation were introduced between monocular and binocular viewing, but when the arrangements were otherwise approximately the same as those of Hochberg and Beck, their results could not be observed. A third experiment demonstrated that the monocularly observed trapezoids did appear slanted.     

液晶显示器上字符辨认效果与观察角度及字符大小的关系

本研究从工程心理学角度,探讨了有源矩阵液晶显示器上字符辨认效果与观察角度及字符大小的关系。实验结果表明：(1)液晶显示的字符辨认效果因观察角度不同而存在显著差异,无论是在水平方向上还是下视方向上,字符辨认错误率均随着观察角度的增大而先慢后快地上升;但相比之下,水平方向上观察角度变化的容许范围大于下视方向上的容许范围;(2)液晶显示器上字符辨认效果也受字符大小的影响,并且字符大小与观察角度之间存在着显著的交互作用;当观察角度较大时,可通过加大字符尺寸来提高视觉辨认效果。     

Journal of experimental psychology: human perception and performance

We examined the nonveridicality of visual direction produced by monocular viewing. In Experiment 1, 19 subjects pointed to a small light and moved a small light to their subjective median plane. The extent of constant error under monocular and binocular viewing conditions differed in both tasks (p less than .001). The monocular-binocular difference was larger when the viewing distance was 25 cm than when it was 50 cm (p less than .01). Also, correlations between phoria and monocular-binocular differences ranged from .58 to .77, depending on viewing distances and tasks. The effects of phoria within the context of Hering's .001). The monocular-binocular difference was larger when the viewing distance was 25 cm than when it was 50 cm (p less than .01). Also, correlations between phoria and monocular-binocular differences ranged from .58 to .77, depending on viewing distances and tasks. The effects of phoria within the context of Hering's .001). The monocular-binocular difference was larger when the viewing distance was 25 cm than when it was 50 cm (p less than .01). Also, correlations between phoria and monocular-binocular differences ranged from .58 to .77, depending on viewing distances and tasks. The effects of phoria within the context of Hering's principle of visual direction can account for these results. In Experiment 2, the same subjects adapted to phoria-induced error by placing a finger over a monocularly viewed target. The difference in their pointing responses before and after the task were reliable (p less than .005), and the correlations between phoria and the pre- to posttest differences were .45 and .77, depending on the number of adaptation trials. We argue that all monocular experiments dealing with visual direction should control for these effects.     

Achromatic color matching as a function of apparent target orientation,target and background luminance,and lightness or brightness instructions

In two experiments, achromatic color matches for a fixed target, under constant illumination, were compared under conditions where the target appeared perpendicular to illumination direction and coplanar with the background (monocular viewing) and where the target appeared nonperpendicular to illumination direction and noncoplanar with the background (binocular viewing). Contrary to the coplanar ratio hypothesis, which predicts a “lightening” of the target seen coplanar with a darker background, a general “darkening” of the target occurred for both white (N9.5/) and black (N3/) backgrounds and for both dark (N5.5/) and light (N6.5/) targets. This darkening effect was greatest for the darker target and black background, and approximately equal for other combinations of target value and background. The direction of the darkening effect is consistent with the albedo hypothesis, which assumes an inferential correction for changes in conditions of illumination. However, variation in the magnitude of the darkening effect is problematical, and cannot be easily explained by any existing theory. In both experiments, instructions to judge “lightness” or “brightness” failed to produce any substantial differences in performance, although postexperimental questioning suggested that subjects had a verbal understanding of these concepts. Apparently, under reduction conditions, subjects lack cues to illumination and make only lightness matches, regardless of instructions.     

Movement and illumination factors in adaptation to prismatic viewing

While wearing laterally displacing prisms, Ss were required to align a spot of light to the phenomenal straightahead. These measurements were obtained at the beginning and at the end of an exposure to prismatic displacement. In addition, Ss either actively controlled movement of the spot of light, or movement was manipulated by E under the direction of the S. Aftereffects were determined by having S position the spot of light with normal vision at the beginning of the experiment and after each measurement obtained under prism viewing. Ss in the darkened room condition who were required to align the spot of light actively showed a significant aftereffect in the direction of prismatic displacement both at the beginning and at the end of the exposure period. No difference in the degree of adaptation was found between those measurements at the beginning and at the end of the exposure period. No significant aftereffects were found when the room was illuminated during prism exposure or when E controlled movement of the light source.     

Perceptual differentiation of sequential visual patterns

The aftereffects of viewing diagonal lines for 50, 500, and 1,000 msec were measured by the speed and accuracy of identification of a variably tilted test grating. Significant RT and tilt aftereffects were found as functions of the duration of orientation-specific adaptation and the angle of separation between inspection and test lines. The results throw light on anchoring effects of the main visual coordinates and support a structural interpretation of orientational selectivity in human vision.     

As the cube turns: Evidence for two processes in the perception of a dynamic reversible figure

The reported reversals of a rotating Necker cube, which changes direction of rotation when a perspective reversal occurs, were examined under a number of conditions. These permitted comparisons of reversal rates within viewing periods, across successive viewing periods within an experimental session, and across successive weekly sessions. In addition, observers viewed either one or two rotating cubes simultaneously within each of the various viewing periods. Clear evidence for a learning effect was obtained in the form of significant savings across successive viewing periods and sessions. At the same time, results from the multiple-cube conditions and from the pattern of reversals within individual viewing periods appeared to be more consistent with a process of neural fatigue. A two-stage model of reversible-figure perception is proposed which is characterized by (1) fatiguing with extended viewing of the two sets of neural channels that underlie the two percepts of the reversible figure, and (2) learning, which helps to establish the organization of the cortical channels as well as moderate channel activity via such processes as attention and strategy.     

Motion adaptation from surrounding stimuli.

When a narrow uniform gap was surrounded by a moving grating, the gap appeared as a grating in the opposite phase to that of the surround, moving in the same direction with the same speed. Contrast thresholds for moving test-gratings placed in the region of the uniform gap were found to be elevated after prolonged viewing of this pattern, thus demonstrating the existence of motion adaptation in a retinal region surrounded by, but not covered by, a moving pattern. The amplitude of the moving induced-grating was measured by nulling with a real grating moving in the same direction and with the same speed as the surround. When the speed of the inducing grating was varied, the amplitude of the induced effect did not correlate with the magnitude of the threshold elevation. Therefore, it is unlikely that motion adaptation in the uniform gap was due to induced gratings. In some conditions, the adaptation effect of surrounding gratings was no less than the adaptation effect of gratings covering the test region. This result rules out an explantation involving scattered light, and indicates that motion adaptation occurs at a later stage than that consisting of simple motion mechanisms which confound the contrast and velocity of a moving stimulus.     

ADAPTATION EFFECTS AND AFTER EFFECTS OF MOVING PATTERNS VIEWED IN THE PERIPHERY OF THE VISUAL FIELD

Different patterns of figures moving behind a window were viewed by subjects while fixating a point 8.5–11° visual angle NW of the display. With prolonged viewing and small figures, the motion appeared to stop completely. With moving figures which stretched the whole way across the field, perpendicular to the direction of motion, a pulsating or wave motion was experienced. A reduction in the number of moving figures was also reported with all the patterns. When the stimulus motion was stopped, the expected after effect of motion in the opposite direction was usually experienced, although in many cases the stopping of the stimulus motion led to an immediate disappearance of the stimulus figures.     

The interplay between stereopsis and structure from motion

In a series of psychophysical experiments, an adaptation paradigm was employed to study the influence of stereopsis on perception of rotation in an ambiguous kinetic depth (KD) display. Without prior adaptation or stereopsis, a rotating globe undergoes spontaneous reversals in perceived direction of rotation, with successive durations of perceived rotation being random variables. Following 90 sec of viewing a stereoscopic globe undergoing unambiguous rotation, the KD globe appeared to rotate in a direction opposite that experienced during the stereoscopic adaptation period. This adaptation aftereffect was short-lived, and it occurred only when the adaptation and test figures stimulated the same retinal areas, and only when the adaptation and test figures rotated about the same axis. The aftereffect was just as strong when the test and adaptation figures had different shapes, as long as the adaptation figure contained multiple directions of motion imaged at different retinal disparities. Nonstereoscopic adaptation figures had no effect on the perceived direction of rotation of the ambiguous KD figure. These results imply that stereopsis and motion strongly interact in the specification of structure from motion, a result that complements earlier work on this problem.     

Absence of color-selectivity in Duncker-type induced visual movement

Using a stationary target and moving field, both consisting of gratings of vertical light and dark bars, Over and Lovegrove (1973) reported that, with monoptic viewing, induced target movement is weaker when the light bars of the two components are different in color. This reduction did not occur for dichoptic viewing, for which the aftereffect was almost negligible. Six experiments are described. The effect of different colors was not confirmed, using a stationary point and moving frame or stationary and moving gratings. Reduced effects for different colors and greatly reduced effects for dichoptic viewing occurred only when there was a stationary boundary to the moving bars of the field grating, as in Over and Lovegrove’s experiment. It is concluded that the effect studied by Over and Lovegrove is not the classical induced movement described by Duncker (1929/1938) but one due to periodic coincidence and noncoincidence of moving and stationary bars in grating patterns. This effect is absent when target and field bars are rendered more distinguishable by different colors.     

Dark adaptation and the Hermann grid illusion

The latency of the perception of the dark spot at the intersection of a Hermann grid was measured before and after dark adaptation. It was found that dark adaptation significantly increased the latency of perception of the spot while light adaptation had no effect. This finding was predicted from the Jung and Spillman account of the Hermann grid illusion and from the Kuffler et al. finding that inhibitory receptive fields of the cat’s retinal ganglion ceils are reduced in size and responsiveness after dark adaptation. The significance of this finding in relation to other simultaneous contrast phenomena is discussed.     

Geometry or not geometry? Perceived orientation and spatial layout in pictures viewed at an angle

Cutting (1988) suggests that changes in the perceived orientations of pictured objects that occur with changes in viewing angle are caused by the geometrical changes that accompany these changes in viewing angle. His geometrical analysis does predict the differential rotation effect reported by Goldstein (1979, 1987), but fails to predict other important aspects of the data. Cutting's analysis does, however, support Goldstein's (1987) conclusion that in future research on picture perception it is important to clearly distinguish between the attributes of perceived orientation and spatial layout.     

Target distance and adaptation in distance perception in the constancy of visual direction

Hay and Sawyer recently demonstrated that the constancy of visual direction (CVD) also operates for near targets. A luminous spot in the dark, 40 cm from the eyes, was perceived as stationary when S nodded his head. This implies that CVD takes target distance, as well as head rotation, into account as a stationary environment is perceived during head movements. Distance is a variable in CVD because, during a turning or nodding of the head, the eyes become displaced relative to the main target direction, the line between the target and the rotation axis of the head. This displacement of the eyes during head rotation causes an additional change in the target direction, i.e., a total angular change greater than the angle of the head rotation. The extent of this additional angular displacement is greater the nearer the target. We demonstrated that the natural combination of accommodation and convergence can supply the information needed by the nervous system to compensate for this additional target displacement. We also found that wearing glasses that alter the relation between these oculomotor adjustments and target distance produces an adaptation in CVD. An adaptation period of 1.5 h produced a large adaptation effect. This effect was not entirely accounted for by an adaptation in distance perception. Measurements of the alteration between oculomotor cues and registered distance with two kinds of tests for distance perception yielded effects significantly smaller than the effect measured with the CVD test. We concluded that the wearing of the glasses had also produced an adaptation within CVD.     

Skin Tone,Crime News,and Social Reality Judgments: Priming the Stereotype of the Dark and Dangerous Black Criminal1

An experiment examined the extent to which viewers’ emotional discomfort with a crime story and perceptions and memorability of a perpetrator and victim could be influenced by the race and skin tone of the perpetrator portrayed in a newscast. Participants were exposed either to a White, light–skinned Black, medium–skinned Black, or dark–skinned Black perpetrator. In addition, participants provided self–reports of their news viewing habits. Results revealed that heavy television news viewers were more likely than light viewers to feel emotional discomfort after being exposed to the dark–skinned Black perpetrator. Heavy news viewers also had favorable perceptions of the victim when the perpetrator was Black, regardless of skin tone. Results also indicated that all participants, regardless of prior news exposure, found the perpetrator more memorable when the perpetrator was a dark–skinned Black male. The methodological and theoretical implications of these findings are discussed.     

Anisotropic perception of visual angle: implications for the horizontal-vertical illusion, overconstancy of size, and the moon illusion.

Three experiments investigated anisotropic perception of visual angle outdoors. In Experiment 1, scales for vertical and horizontal visual angles ranging from 20 degrees to 80 degrees were constructed with the method of angle production (in which the subject reproduced a visual angle with a protractor) and the method of distance production (in which the subject produced a visual angle by adjusting viewing distance). In Experiment 2, scales for vertical and horizontal visual angles of 5 degrees-30 degrees were constructed with the method of angle production and were compared with scales for orientation in the frontal plane. In Experiment 3, vertical and horizontal visual angles of 3 degrees-80 degrees were judged with the method of verbal estimation. The main results of the experiments were as follows: (1) The obtained angles for visual angle are described by a quadratic equation, theta' = a + b theta + c theta 2 (where theta is the visual angle; theta', the obtained angle; a, b, and c, constants). (2) The linear coefficient b is larger than unity and is steeper for vertical direction than for horizontal direction. (3) The quadratic coefficient c is generally smaller than zero and is negatively larger for vertical direction than for horizontal direction. And (4) the obtained angle for visual angle is larger than that for orientation. From these results, it was possible to predict the horizontal-vertical illusion, over-constancy of size, and the moon illusion.     

Dual adaptation of apparent concomitant motion contingent on head rotation frequency

Perceived movement of a stationary visual stimulus during head motion was measured before and after adaptation intervals during which participants performed voluntary head oscillations while viewing a moving spot. During these intervals, participants viewed the spot stimulus moving alternately in the same direction as the head was moving during either .25- or 2.0-Hz oscillations, and then in the opposite direction as the head at the other of the two frequencies. Postadaptation measures indicated that the visual stimuli were perceived as stationary only if traveling in the same direction as that viewed during adaptation at the same frequency of head motion. Thus, opposite directions of spot motion were perceived as stationary following adaptation depending on head movement frequency. The results provide an example of the ability to establish dual (or “context-specific”) adaptations to altered visual—vestibular feedback.     

Matching the rate of concurrent tone bursts and light flashes as a function of flash surround luminance

Subjects adjusted the rate of a repeating toneburst to match that of a concurrently flashing light, or vice versa. Flashes were viewed in luminous or wholly dark surrounds. Matches usually departed from veridical rate matches, and always were affected in the same direction by changes in surround luminance. Matches were a function of whether subjects controlled the visual or auditory stimulus; also, subjects usually reported “driving” of flash rates by auditory rates when they controlled tone rate, but not when they controlled flash rate.