Perceived duration as a function of pitch

It was demonstrated with 7 observers that the duration of a high frequency tone was perceived to be longer than the duration of a low frequency tone, even though the actual duration of the two tones was equal.     

Target size and luminance in apparent brightness of the peripheral visual field.

Four target sizes between 15 and 120 min. of arc with six luminance levels covering the range between 398.1 and 1.26 cd/m2 in steps of .5 log units were presented to 0, 20, 40, 60, and 80 degrees nasal retinal loci. In both peripheral and foveal viewing, magnitude estimates to apparent brightness judged by 12 Ss changed as a function of target size and luminance. The exponent of the power function was not dependent on retinal loci but on target size. However, when target size increased, the apparent brightness was slightly greater with peripheral viewing than with foveal viewing.     

The luminance of tachistoscope lamps as a function of flash duration

The steady-state luminance of the lamps in a commonly used Iconix tachistoscope was shown to depend, in a complex nonlinear fashion, upon the length of time the lamps were lit. This was probably due to variations in lamp temperature with time. An integrating photometer was used to measure the light energy present in short flashes and in time periods of various durations with the lamps burning continuously. The equivalent luminance of short flashes was calculated by comparing values obtained by integration over a short flash with values resulting from integration, over an identical duration, of the lamps in a steady-state. With flashes up to 50 msec in nominal duration, luminous energy was less than one-half of that present in the same duration with the lamps burning continuously. The importance of this information for the interpretation of tachistoscopic experiments, as well as possible means of monitoring the effects, are discussed.     

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.     

Threshold exposure duration as a function of luminance for visual recognition

Threshold exposure duration was measured at set luminances for recognition at successively higher criteria of 1, 2, 3, 4, and 5 correct letters in nonsense words. Two sizes of letters were used and triads of Landolt “Cs” were compared with letters. Tachistoscopic procedures were the typical ascending seriesin the method of limits and pre- and postexposure light adaptation. Obtained log t vs log I functions were two-part straight line curves both describable by the equation, log t + log I^k = log C, but with k and C abruptly changing at a certain I. Reciprocity (k = 1) held only for low Is and the low criterion; as criterion was raised at low Is k became less negative (about ?.60 at five correct) for both sizesand for “Cs.” At higher Is, k shifted from ?.25 to ?.40 with increasing criterion for large letters, but variedaround ?.45 at all criteria for small. The lower the criterion, the lower the / and t at which k and C abruptly changed for large letters, but only t was lower for small. Changes in t with acuity requirement change, and from one criterion level to the next, were not uniform over all Is. Results may reflect obscuring procedural factors or basic properties of visual recognition processes. Some interpretations in terms of procedural variables are offered. It appears more likely that visual recognition involves central processes for which time is needed in excess of that for summation of luminances for mere detection by sensory processes, as expressed in Bloch s’ reciprocity law.     

Illusion magnitude as a function of visual field exposure

Forty-eight right-handed subjects divided into four groups, each consisting of six males and six females, were employed in an investigation of cerebral hemispheric influence on the perception of tachistoscopically presented simultaneous and successive versions of the Mueller-Lyer figure. The simultaneous version exposed in the left visual field resulted in a larger effect than did right visual field exposures. The successive version exposed in the right visual field resulted in a larger illusion magnitude than it did in the left visual field. The magnitude of visual field differences in response to the successive version was greater than visual field differences found in response to the simultaneous version     

Perceived target displacement as a function of field movement and asymmetry

In two experiments induced movement of an object was produced to demonstrate that movement of the background influences the perceived localization of the object in space. The Roelofs (asymmetry) effect could be used to explain only part of the shift in localization in Experiment1. The asymmetry effect was excluded from Experiment2 by the procedure employed. It was concluded that the Roelofs effect is a sufficient, but not necessary, condition for the effects of induced movement to occur, and that relative displacement of the target and background plays an important part in the illusion. Furthermore, it was shown that the effects of induced movement can occur even when the border of the background remains stationary.     

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.     

Variations in watch keeping performance as a function of the rate and duration of visual signals

This study was designed to assess the relative effects on watch keeping performance of five signal durations (0.5, 1.0, 2.0, 4.0, and 8.0sec) combined factorially with five signal rates (6, 12, 24, 48, and 96 sig/h). A visual display consisting of a red and green light mounted on a vertical vector was used; red-onset and green-offset were critical signals. The probability of correct detections increased monotonically with increases in signal duration; a stable rate of nearly 100% detection was approached at signal durations of 4.0 and 8.0 sec, independently of signal rates. The likelihood of detection was enhanced by increases in signal rates only at the 0.5-sec duration with the green-offset critical signal. Response time to correct detections increased with time on watch, independently of signal rates and durations.     

Perceived duration,visual persistence,and neural integration

Varying stimulus intensity while measuring the perceived duration/visual persistence of brief light flashes has yielded disparate results. Some studies have found a direct relationship between the two variables; others have found an inverse relationship. Several models have been suggested to unify this behavioral literature. They invoke the absolute intensity and the nature of the judgment as explanatory variables. We now present physiological data whose analysis was motivated by these models. We measured the duration of photoreceptor potentials as a function of light intensity and response measure. One response measure was. the length of time required for the response to decline from the peak by a criterion amount. The other response measure was the length of time a response stayed above a criterion level. These data suggest that each behaviorally based model captured a different aspect of a single underlying mechanism and that a melding of the two critical concepts would harmonize all of the results: In this melding, the sensory signals that mediate visual perception would have the type of complex intensity- and time-dependent properties found in real neural responses.     

Orientation sensitivity in the peripheral visual field

Orientation sensitivity in the peripheral visual field has been tested in two tasks: (a) setting horizontal the orientation of a grating at various retinal eccentricities, and (b) matching the orientation of a peripherally viewed grating as close as possible to an oblique reference viewed foveally. Both performances fall off with increasing retinal eccentricity. Magnification of the stimulus optimizes peripheral performance. Peripheral performance, optimized by magnification, varies with retinal eccentricity. It approaches, but does not reach, the foveal value (tested by the same method) at 10 deg of eccentricity, and is much lower at 20 and 30 deg of eccentricity.