DO HUMANS POSSESS AN INTERNAL CLOCK WITH SCALAR TIMING PROPERTIES

The question of whether humans possess an internal clock with scalar timing properties was discussed with reference to three sorts of experiments. First, evidence from experiments on interval production was presented which showed that interval production by humans that is not based on chronometric counting exhibited approximate scalar properties as (i) mean times produced increased linearly with real time, and (ii) coefficients of variation of times produced varied unsystematically (in the range 0.10 to 0.16) as the time produced varied. Second, an experiment measuring the intercount units used by subjects in chronometric counting revealed that count units exhibited approximate scalar properties, with their coefficient of variation remaining roughly constant (in the range 0.10 to 0.14) as intercount interval changed. A simple model of chronometric counting based on scalar properties of count units was shown to be compatible with the declining coefficients of variation with increases in interval produced found in the overall time judgments based on chronometric counting. Finally, two experiments with normal humans which were analogs of animal experiments on interval bisection and temporal generalization were discussed. Here, human performance differed from that found in animals in both cases, suggesting that the way humans make judgments about intervals differs systematically from the judgmental processes of animals, but models of behavior consistent with underlying scalar representations of duration could be developed. Overall, all three sorts of experiments produced evidence suggesting that human timing can, in some circumstances, be described well by a scalar timing mechanism. © 1991.