Efficient across-frequency integration: Evidence from psychometric functions

Across-frequency integration of complex signals was investigated by measuri ng psychometric functions [log(d') versus signal level in dB SPL] for detec tion of brief and long signals presented in broadband noise. The signals we re tones at 630, 1600, and 4000 Hz, and a nine-tone complex with components spaced at one-third-octave frequencies between 630 and 4000 Hz. The phase relationship of the components in the complex was varied such that adjacent components were in phase (at 0 degrees), 90, or 180 degrees out of phase. Signal durations (defined in terms of the number of cycles between the half -amplitude points of the Gaussian envelopes) of 4.7 and 150 cycles were tes ted. Results for six normal-hearing listeners showed that the slopes of the psychometric functions were steeper for the brief than for the long signal s, and steeper for the tone complexes than for the tones, particularly for the brief signals. This suggests that the transformation from signal intens ity to decision variable may be different for brief complex signals than fo r tonal signals and long complex signals. Thresholds obtained from the psyc hometric functions were in excellent agreement with those obtained with an adaptive procedure that employed three interleaved tracks. For the long sig nals, the threshold improvement for the tone complexes relative to a single tone was well described by a 5* log(n) integration rule. However, the thre shold improvement for brief signals obeyed a more efficient integration rul e of 7 to 8 * log(n). A portion of this effect could be accounted for by th e phase relationship of the tone complexes; thresholds for brief signals we re lowest when the components were in phase at the envelope peak of the sig nal. This finding indicates that temporal synchrony across auditory channel s may enhance detection of brief multi-tone complexes. (C) 2000 Acoustical Society of America. [S0001-4966(00)05806-9].