Control of responding by location of auditory stimuli: adjacency of sound and response.

Four rhesus monkeys were trained to respond on one key when a one-second noise burst was presented through one speaker and to respond on a second key when the noise burst was presented through a second speaker. The acquisition of stimulus control was studied under three conditions, in each of which the relationship between the sound source and the response-key positions varied: an adjacent condition in which the noise burst was presented through the key and a response on this key was reinforced; a reversed-adjacent condition in which the noise burst was presented through one key and responding on the other key was reinforced: and a nonadiacent condition in which responding on the key nearer the sound was reinforced. Under adjacent conditions, stimulus control developed within one or two sessions. Under reversed and nonadjacent conditions, 10 sessions were required for the development of control. The asymptote of correct responding was the same under each condition in all animals.     

Variable Perception of White Noise in Ambiguous Phonetic Contexts: The Case of /p/ and /f/

The roles of spectro-temporal coherence, lexical status, and word position in the perception of speech in acoustic signals containing a mixture of speech and nonspeech sounds were investigated. Stimuli consisted of nine (non)words in which either white noise was inserted only into the silent interval preceding and/or following the onset of vocalic transitions ambiguous between /p/ and /f/, or in which white noise overlaid the entire utterance. Ten listeners perceived 85% /f/s when noise was inserted only into the silent interval signaling a stop closure, 47% /f/s when noise overlaid the entire (non)words, and 1% in the control condition that contained no noise. Effects of spectro-temporal coherence seemed to have dominated perceptual outcomes, although the lexical status and position of the critical phoneme also appeared to affect responses. The results are explained more adequately by the theory of Auditory Scene Analysis than by the Motor Theory of Speech Perception.