Spectral and temporal integration of brief tones.

Both spectral and temporal integration of tones have been explored in detail, but integration of tones varying across both dimensions has received little attention. This study explores temporal integration of tone pulses that vary over a range of frequencies. Baseline thresholds were obtained for both spectral and temporal integration with the same signals and compared with prior research. The signals were then varied on both dimensions in several ways: with equivalent spectral and temporal step sizes, different spectral and temporal step sizes, and a random pattern of frequency presentation. The data were also analyzed by spectral step size, temporal step size, frequency range, direction and slope of frequency change, and predictability. The spectral and temporal integration conditions showed that the current procedures and signals yielded the same improvement in detection thresholds as prior studies. The spectrotemporal integration conditions showed the improvement for overall detection of the signals to be limited by spectral integration, with improvement related primarily to the number of tones, regardless of timing and frequency. Surprisingly, trial-by-trial random presentation of signal frequencies did not negatively influence detection. These results support the multiple looks hypothesis [Viemeister, N. F. and Wakefield, G. H. (1991). "Temporal integration and multiple looks," J. Acoust. Soc. Am. 90, 858-865] as applied to spectrotemporal integration.