Time perception: effects of sensory modality, ambient illumination and intervals.

Delay and Richardson (3) reported that high ambient illumination shortened their subjects' estimates of 15-sec. intervals via the method of oroduction. These results are the reverse of the well known lengthening phenomena associated with auditory stimulation (4). Hocherman and Ben-Dov (5) postulated modality-specific clocks that may alter our time perceptions. The present study was done to expand the findings of Delay and Richardson (3). By using both visual and auditory boundaries, two modalities were compared. Although the general levels of illumination remained the same, four Uferent durations were used in this srudy. The psychophysical method of production was replaced by the method of reproduction in the present study for theoretical reasons (2). Observers, 12 men and 12 women, participated. They were students of psychology from an urban Southern Cahfornia population, with a median age of 18 yr. The observers looked at a computer monitor that presented intervals "bounded" by either the visual cursor or auditory tones. The intervals were 9, 18, 27, or 36 sec. Following interval presentations, a "start" signal (same modality) began the reproduction period and the observers pushed a button to indicate the end of this "reproduction" of the original interval. Three levels of ambient illumination were tested: dark (<.22 lux), low (86 lux) and high (170 lux). The experiment was conducted as a 2 x 3 x 4 (modality x ambient illumination level x intervals) design with repeated measures on the last factor. The over-all F comparing the two sensory modalities was nonsignificant although the auditorially bounded intervals were judged longer than the visually bounded intervals (Auditory M = 22.1, SD = 5.6; Visual M = 18.9, SD = 9.9). The F ratios for differences among the three levels of ambient illumination were also nonsignificant. Of course, the I.' comparing the four intervals was sigdicant F,,,4 = 47.85, p < . 0 1 ) Another significant F was obtained for the interaction of modality x duration (F,,,, =23.10, p<.01). Both the auditory and visual groups overestimated the 9-sec. interval and underestimated the 27-sec. and 36-sec. intervals. On the 18-sec. interval there was a split; the auditory group overestimated (M = 21 sec.) and the visual group underestimated (M = 17 sec.). Generally speaking, these results do not sustain the findings of Delay and Richardson (3). In this study the ambient illumination levels did not alter the perceptions of duration. There could be many reasons for this: (a) although the illumination (lux) levels were controlled, the spectral characteristics may have differed in the two studies. (b) The psychophysical method of reproduction employed here may have made an important difference. Using the psychophysical method of reproduction (rather than "production") seemed a logical step based on previous research on time-perception methodology (1, 2). I t reduces the time-order-error. The significant interaction in the present study is related to the findings of Sebel and Wilsoncroft (6) and verifies the psychophysical complexity of measuring time perception under the most simple environmental conditions. Further research is urgently needed to ascertain the role of ambient illumination on human time perception in social, medical, and special environments.