Tonal Signal Detection under Various Light Stimulation Conditions

Abstract

Using forced-choice, a tonal signal was presented under several photic conditions. In one experiment, binocular exposure to a strong light had 0.25 sec duration as had 4 white-noise bursts (60 dB SPL) per trial—one burst coincident with the signal. Onset times of light exposures were 0.50 or 0.25 sec before noise bursts, concurrent with them, or immediately following. One run of 48 consecutive trials under each photic condition along with a control run comprised an experimental set. A later experiment, similar except for shortened periods (0.20 sec) and for maintenance of white noise at 60 dB, provided light onsets 0.20 sec before, coincident with, or immediately following the possible signal periods. A two-level light intensity variable was also included. With noise bursts, all condition means (48 sets) fell within a range of 5.3 in percentage correct responses. Here, the small advantage favored light coincident with possible signal periods (3 of 6 subjects conforming). Detectability of the signal in steady noise was significantly lower when light followed possible signals. Detectabilities were independent of light intensity variable. Results were discussed in relation to findings of Child and Wendt [J. Exptl. Psychol. 23, 109–127 (1938)1 and others.