Detectability of auditory signals presented without defined observation intervals

Ability to detect tones in noise was measured without defined observation intervals. Latency density functions were estimated for the first response following a signal and, separately, for the first response following randomly distributed instances of background noise. Detection performance was measured by the maximum separation between the cumulative latency density functions for signal-plus-noise and for noise alone. Values of d′, estimated by this procedure, were approximately those obtained with a 2-dB weaker signal and defined observation intervals. Simulation of defined- and nondefined-interval tasks with an energy detector showed that this device performs very similarly to the human listener in both cases. Subject Classification: 4365.58, 4365.75, 4365.50, 4365.68.