TEMPORAL BISECTION IN HUMANS WITH LONGER STIMULUS DURATIONS

Normal adults were tested in eight temporal bisection conditions, usin g 500-Hz tones as stimuli. Stimulus lengths matched, or overlapped wit h, durations normally used in bisection experiments with animals, and chronometric counting was prevented by using a concurrent digit-shadow ing task. Four experimental groups were used to investigate any effect s of stimulus spacing, and stimuli were logarithmically or linearly sp aced between standard ''short'' and ''long'' durations of 1 and 4, or 2 and 8 sec. A slight leftward shift of the psychophysical function wa s found in the logarithmic spacing condition, relative to linear spaci ng. Four other groups tested the conjecture that the ratio of the shor t and long standards might play some role in determining the location of the bisection point, and conditions with long/short ratios of 2: 1 and 5: 1 were used. In all cases the bisection point was close to the arithmetic mean of the short and long standards, rather than the geome tric mean, as in animal studies. Overall, however, smaller long/short ratios (which may indicate more difficult temporal discriminations) pr oduced more sensitive timing. When the long/short ratio was held const ant, however, data showed nearly perfect superimposition, indicating c onformity to scalar timing. In general, results were similar to those from experiments with humans that used much shorter durations, indicat ing the animal/human differences in bisection do not depend on the abs olute lengths of the stimuli used.