Echoic memory in the rat: effects of inspection time, retention interval, and the spectral composition of masking noise.

Memory for tones (1100 vs. 2330 Hz) was studied in 4 rats (Rattus norvegicus), as affected by the durations of both target tones (30 to 620 ms) and noise-filled retention intervals (0 to 480 ms). With a 0-ms delay, performance was near asymptotic with the 30-ms tone, but the memory of this brief tone suffered a massive decrement at retention intervals as brief as 60 ms; in contrast, memory for the 340-ms tone was stable for at least 240 ms. If the retention interval was filled by band-stop noise (with targets presented in the spectral gap), then the rat's memory for brief tones was superior to that obtained with the standard broad-band noise filler, and band-stop noise was better than a band-pass noise that had the tones embedded in the region of its spectral energy. These findings are consistent with the hypotheses that auditory memory in the rat consists of a transient sensorylike echoic store and a short-term store more resistant to the effects of retroactive interference.