Fig. 2.
Behavioral results (experiment 1). (A) Detection times for RAND-REG and REG-RAND transitions where REG patterns consisted of 10 tones (Rcyc = 10). Bar plots show the mean RT as measured relative to the nominal transition time. The total height of the bars corresponds to the raw RTs from which the RT to the STEP condition (hatched bars) was subtracted to obtain baselined RT (solid bars). Error bars indicate 1 SD. Also plotted are RT histograms for RAND-REG (Upper) and REG-RAND (Lower). The histograms were computed over all trials and all subjects. Raw RT in each trial was corrected by that subject’s mean STEP RT (thus resulting in instances of negative RT, or responses occurring before the nominal transition in RAND-REG). Orange or dark-blue colored bars indicate responses which fell within 2 SDs from the mean. The results demonstrate that, on average, subjects require about 1.5 cycles to detect the emergence of regularity (with >80% of the responses occurring before the pattern has repeated). The average time required to detect the violation of a REG pattern is three tones. (B) Detection times for RAND-REG and REG-RAND transitions where REG patterns consisted of 20 tones (Rcyc = 20). (C) Ideal observer model responses to RAND-REG signals showing the average information content of each tone-pip (from five tones before the transition). The model required a cycle + four tones to detect the emergence of regularity. Shading indicates 2 SEM. (D) Ideal observer model responses to REG-RAND signals showing the average information content of each tone-pip (from five tones before the transition). Transitions are detected immediately following the first RAND tone.