Brightness enhancement and the Talbot level in stationary gratings

At low spatial frequencies, the perceived brightness of the light phase of a stationary square-wave grating is greater than the brightness of a solid field of equal physical luminance. That increase in the perceived brightness of a grating at low spatial frequencies is analogous to the brightness enhancement observed in a flickering light at low temporal frequencies. At or above the critical spatial frequency—the visual resolution threshold—the brightness of a grating is determined by its space-average luminance, just as the brightness of a flickering light at or above the critical flicker frequency is determined by its time-average luminance in accordance with Talbot’s law. Thus, Talbot’s law applies in the spatial as well as the temporal domain. The present study adds to the evidence that temporal and spatial frequency play analogous roles in some aspects of brightness vision.     

Brightness constancy in a Ganzfeld environment

In this paper, experiments are described in which brightness constancy was studied in a Ganzfeld environment. Luminance variation by means of neutral density filters was applied to stimuli consisting of a Ganzfeld with superimposed disks. To this end, a special-purpose apparatus was constructed. Sequential dichoptical brightness matches with a reference stimulus were carried out for the disks as well as the homogeneous surround. The results of these measurements indicate that (1) besides a clear tendency toward brightness constancy, small but systematic effects of the average luminance level are present and (2) the brightness of the Ganzfeld is hardly affected by the presence of the disks. Finally, it is shown that the experimental results can be modeled adequately in terms of a concept that involves an accumulation of contrast information.     

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.     

Brightness contrast effects in a pupillometric experiment

The effect of depth displacement of test bars from the induction wedge of the Ponzo illusion was investigated in two experiments. Either two wedges of opposite orientation were presented simultaneously, one at a near and the other at a far distance, or only one wedge was presented at either the near or the far distance. The test bars were stereoscopically either in the plane of the wedge or displaced from the wedge in distance. When the two wedges were presented simultaneously, the direction of the Ponzo illusion was determined by the wedge at the same perceived distance as the test bars. When only one wedge was present, stereoscopic displacement of the bars in front of, but not behind, the wedge decreased the magnitude of the illusion. The results are interpreted in terms of the adjacency principle.

     

The patterns seen when alternating electric current is passed through the eye

When alternating current of frequency up to 210 c's. is passed through the eye while the retina is brightly and uniformly illuminated, conspicuous spatial patterns are seen. Other such patterns are seen when current of frequency up to 100 c/s. is passed through the eye in darkness. These patterns are here described, and their origin is discussed.     

The termination phase of psychoanalysis as seen through the lens of the dream

The decision about when to terminate analysis has long been underpinned by a theory-driven criterion model, which may steer the analytic dialogue away from its customary activities of free association, empathic listening, and interpretation. As a remedy to this situation, the author proposes that by paying careful attention to less consciously crafted patient communications such as dreams, the analytic dyad can consider readiness to set a termination date from a perspective that is context-sensitive and less encumbered by preordained criteria. Tracing the dreams of one analysand from the vantage point of contemporary dream theory, the author demonstrates how careful attention to the dream elucidated the patient's readiness to terminate and her complex feelings about the termination process. Finally, the author challenges the notion that the termination phase is of greater evaluative than therapeutic importance, and provides clinical material as evidence that this is not the case.     

Visual recognition memory enhancement in children through differential outcomes

Objective

The use of differential outcomes has been shown to enhance discriminative learning and face recognition in children and adults. In this study, we further investigated whether the differential outcome procedure (DOP) would also be effective in improving recognition memory for a wide range of stimuli with varying visual complexity (familiar objects, abstract stimuli, and complex scenes) in 5- and 7-year-old children.

Method

Participants viewed a sample stimulus and, after a short (5 s) or a long (15 s) delay, they had to identify the previously seen stimulus among four choice alternatives. In the differential outcomes condition, each sample stimulus was paired with a specific outcome; whereas in the non-differential conditions outcomes were administered randomly. In Experiment 2, we replicated Experiment 1 but in addition we asked participants to perform an articulatory suppression task to prevent verbal rehearsal.

Results

Children showed a greater overall visual delayed recognition when differential outcomes were arranged in both experiments. The type of stimulus being used modulated this effect; a beneficial effect of the differential outcomes training was evident with abstract objects in Experiment 1 and with both, abstract objects and scenes in Experiment 2.     

... As seen by a social scientist

Pastoral Psychology -     

Brightness scaling of periodic tones

Brightness is an attribute often used by musicians when describing timbral characteristics. It is related to the spectral distribution of energy, as is sharpness, studied by Zwicker (Psychoacoustics: Facts and Models, 1990). In the current work, subjects adjusted the spectral slope and thus the spectral centroid (SC) of one of a pair of sounds to make it twice as bright as the other, so as to build a perceptual scale. The ratio of SC required to double brightness is a little less than 2 and decreases as the SC of the tones increases. For these tones, the ratio of brightness is statistically different from the ratio of sharpness calculated from published models.     

Brightness contrast in the cat

Using both the method of paired comparisons and the method of constant stimuli, degree of brightness contrast was determined for two cats. Brightness contrast varied with relative luminance of various parts of the stimulus configuration in a manner comparable to that found in human Ss; brightness constancy was not obtained. The data indicate a fixed, nonadaptive basic visual process rather than a cognitive or adaptive perceptual constancy.     

Societal risks as seen by a Norwegian public

In two studies, questionnaires originally developed to study risk perception in the United States were administered to Norwegian students. Level of perceived risk in Norway was clearly below American scores for most hazards, but slightly above what has been found in a parallel Hungarian study. Norwegians were more concerned than both Hungarians and Americans about narcotics, but less than Americans about chemicals used in food and agriculture, and less than Hungarians about a number of common, everyday hazards. When ratings on nine risk characteristics were factor analyzed, a two dimensional solution was found with Fatal risk and Involuntary risk as the two most important dimensions. Ratings of general death risk, harm risk, and death risk for those exposed were highly correlated, but appeared to be unrelated to the number of people believed to be exposed to the hazard.     

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.