Communications Biophysics

XV. COMMUNICATIONS BIOPHYSICS Prof. W. A. Rosenblith Prof. R. C. Booton, Jr. Dr. J. S. Barlow* Dr. M. A. B. Brazier* Dr. D. H. Raab

A. E. Albert

N. E. Berg

R. M. Brown

G. S. Fahringer

A. BEHAVIORAL REACTION TIMES TO ACOUSTIC CLICKS

Subjects placed in a dimly-lit anechoic chamber were instructed to press a micro-switch as soon as they heard a click presented to them by an earphone. The click was always preceded by a warning light of fixed duration. The warning light and the click were separated by a variable time interval so that the subjects were not able to antici-pate the click. The data presented below were selected for a time interval of 2. 5 sec between the onset of the warning light and the click; this time interval yielded on the

average the shortest reaction times. The simple reaction times were measured by means of an electronic counter. The subjects were trained separately on clicks approxi-mately 60 db above their respective thresholds until their performance had stabilized. Then simple reaction times were determined for five different intensities of the click.

260 250 240 230 u' 220 o 210 _ 200 Z 190 I 180 0 SUBJECT A SUBJECT B SUBJECT C 0,_ -70 -60 -50 -40 -30 -20

CLICK INTENSITY (DB BELOW REFERENCE LEVEL)

I I I I I I

Fig. XV-1

Mean reaction time vs. click intensity.

From the Neurophysiological Laboratory of the Neurology Service of the Mass-achusetts General Hospital.

-75--10 0 o w Ir + i t't' -0,~ I i I

(XV. COMMUNICATIONS BIOPHYSICS) a SUBJECT A O SUBJECT B 0 SUBJECT C ". -0 0-r-0 -20 -10 0 -80 -70 -60 -50 -40 -30

CLICK INTENSITY (DB BELOW REFERENCE LEVEL)

Percentage of

Fig. XV-2

deviation (standard deviation/mean) vs. click intensity.

Figure XV-1 presents the mean reaction times for three subjects; each point represents at least 100 judgments, but in most instances 200 judgments. (It may, in this connec-tion, be worth while to recall that the onset latency of evoked electrical responses to clicks at the auditory cortex of anesthetized animals is roughly 1/100 sec.)

Figure XV-2 plots the standard deviation as a percentage of the mean (coefficient of variation). _{The data mentioned above were all collected in so-called} "fixed-intensity-runs," that is, in each experimental session clicks were presented at a single intensity level only. _{For one of the subjects we have also data for "mixed-intensity-runs," that} is, for sessions in which the five intensity levels were presented randomly. Compared to the fixed-intensity-run data, there is a tendency toward an increase of the mean reaction time, and there is a consistent increase in the coefficient of variation.

N. E. Berg, A. E. Albert