Harvey A. Taub

PERFORMANCE OF YOUNG AND OLDER DRIVERS ON A STATIC ACUITY TEST UNDER PHOTOPIC AND MESOPIC LUMINANCE CONDITIONS

Sixty young (18−25 years) and 91 older volunteers (60-87 years) were tested for static visual acuity under six different luminance levels ranging from 245.5 cd/m2 (photopic) to 0.2 cd/m2 (mesopic). The results showed significant differences in log decimal acuity and in passing a 20/40 acuity criterion score as a function of age and luminance level. There were no differences, however, in comparisons between young subjects and those aged 60-64. It seems, therefore, that when using visual acuity measures, as is done for driver licensing, 65 years is the critical age after which visual acuity becomes significantly poorer under conditions of degraded illumination. The implications for issuing drivers licenses to individuals over age 65 based on standard visual acuity testing are discussed.

Age-dependent magnitude and time course of early light adaptation

Crawford (1947) demonstrated that large and rapid changes in visual sensitivity accompany an abrupt increase in retinal illumination. This has been referred to as early light adaptation (ELA) in order to distinguish these initial adjustments from those occurring after the eye has become more fully light adapted (White, Kelly, & Sturr, 1978). Although much research has been carried out on ELA, the underlying mechanisms remain unknown. As part of a baseline condition for a recent ELA study in our laboratory (Kelly, 1979), ELA functions were measured on a large homogeneous field. Four observers showed a large threshold rise at the onset of the adapting field, with an exponential decay to steady-state level. However, a fifth observer repeatedly failed to show the large threshold overshoot. Following considerable effort to determine the cause of this difference, we suspected that age might be a major variable. The subject with the anomalous results was 47 years old, whereas all the others were in their 20s. Since there is a growing body of evidence documenting losses in temporal response properties of the aging visual system (Eriksen, Hamlin, & Breitmeyer, 1970; Kline & Orme-Rogers, 1978; Kline & Schieber, 1981; Pollack, 1978; Walsh, 1976), we postulated that the ELA function would also manifest age-dependent changes. This report describes a study designed to test this hypothesis.

KEEPING TRACK OF SEQUENTIAL EVENTS: EFFECTS OF STIMULUS ON-TIME AND INTERSTIMULUS OFF-TIME

Ss were required to keep track of the number of occurrences of each of four different letters (categories) presented sequentially as a function of the total number of letters presented (trial length), the rate of presentation, and the two components which, when combined, constitute the rate, namely, stimulus on-time and the interstimulus interval or off-time. In general, performance varied inversely with trial length and rate of presentation. Of greater importance, however, was the complex interaction between the rate of presentation and the components of that rate. At the fastest rate, performance was relatively invariant as a function of these components; at intermediate rates the shortest on-time led to the best performance, while at the slowest rate the shortest on-time led to the poorest performance. The observed results are explained primarily in terms of the time available for rehearsal.

Early light adaptation in young, middle-aged, and older observers

Early light adaptation (ELA) was examined in young, middle-aged, and older observers in two experiments employing a criterion-free procedure. All subjects had corrected visual acuity of at least 20/30 and no history of ocular pathology. A white, 1.2°, 50-msec test flash (TP) was presented in the center of a white, 8.2° × 7.4°, 1,000-msec photopic adapting field (AF) through an artificial pupil to the left temporal retina. Our results showed a systematic slowing in the time course of ELA: the young group, a steep recovery function; the middle group, a less steep function; and the oldest group, a reversal of the function. The individual data of the young and older observers were characteristic of their groups, but the middle-aged observers showed interesting transitional functions. The possible selective loss of channels in the aging visual system is discussed.

Hypnotizability and Speed of Visual Information Processing

Abstract Following the determination of the luminance threshold of each S, high and low hypnotizable Ss were tested for speed of information processing using a backward masking paradigm with a bias-free and ceiling-free psychophysical task. No significant relationship between hypnotizability as measured by the Stanford Hypnotic Susceptibility Scale, Form A (SHSS:A) of Weitzenhoffer and Hilgard (1959) and speed of information processing was observed. The order of administering SHSS:A, pre- or postthreshold task, was significantly related to luminance threshold. Results were compared to other studies wherein some evidence for a relationship between hypnotizability and speed of visual information processing had been offered.

Keeping Track of Sequential Events: Irrelevant Information and Paced Rehearsal

The effects of irrelevant information on Ss ability to keep track of a changing situation mentally were examined. It appears that, when relevant stimuli are presented at an irregular rate of presentation, irrelevant stimuli interspersed with the relevant stimuli may enable Ss to pace rehearsal of the current state of the changing situation in a fashion that reduces the interference effects of the irregular rate of presentation.

Visual Information Processing Speed in Hypnotized and Nonhypnotized Subjects

Using a backward-masking paradigm with a bias-free and ceiling-free psychophysical task, we tested hypnotized and control subjects for speed of visual information processing. Approximately half of each group received visual imagery suggestions in an attempt to influence attention. Imagery produced no significant differential effect. Although an absence of a hypnotizability-performance relationship was in keeping with findings of a previous study, those subjects in the present study who performed under hypnosis were, as a group, significantly superior to the other subjects in speed of information processing.

Accessibility-a necessary control for studies of essential hypertension: a brief communication.

Abstract A study which was planned to compare the relative effect of relaxation and hypnosis upon essenitial hypertension also offered the opportunity to replicate some of the findings of a previous investigation. A failure in such replication led to consideration of the effect of accessibility to the laboratory, a variable not typically controlled A significant differential effect of easy versus hard access was observed.

Perceived Choice of Prose Materials by Young and Elderly Adults.

Abstract Three experiments evaluated the effects of perceived choice upon comprehension and memory of prose reading passages. Participants in the choice conditions selected the titles of the passages they read, while the rest of the volunteers were not given the opportunity to choose. Experiment 1 compared choice and no choice conditions with young (x = 28.3 years) and elderly (x ‐ 68.9 years) adults of various vocabulary levels. Experiments 2 and 3 tested only elderly groups to evaluate a wider range of vocabulary levels and to compare the effects of starting the reading task either immediately after choosing the titles or after a delay of 2 to 3 weeks. The results indicated both age‐ and vocabulary‐related deficits. However, perceived choice conditions did not produce any consistent improvement in performance.

Spatial Coding of Serial Verbal Input

60 Ss were given 8 lists consisting of 9 consonants each to recall. The letters were presented serially either at the same location on a memory drum, at different locations haphazardly arranged across the viewing slot, or left to right at different locations. Both where and when an S wrote an item during recall were recorded. Although total items recalled remained the same, temporal position recall declined with practice while spatial location recall was sensitive only to whether or not the items had been shown in left to right order. The results indicate that spatial coding of serial verbal input can occur, at least when stimuli are presented in a spatially coherent fashion, and that spatial coding is not necessarily derived from temporal ordering of the stimuli in memory.