Biomedical subjects

Stephen McAdams

Publications and source records attributed to Stephen McAdams.

4 recordsLinked to original sources

PubMed2003

Postrecognition of interleaved melodies as an indirect measure of auditory stream formation.

Primitive processes involved in auditory stream formation are measured with indirect, objective method. A target melody interleaved with a distractor sequence is followed by a probe melody that was identical to the target or differed by 2 notes. Listeners decided whether the probe melody was present or not in the composite sequence. Interleaved melody recognition is not possible when distractor sequences have the same mean frequency and maximum contour crossover with target melodies. Performance increases with mean frequency separation and timbral dissimilarity and is unaffected by the duration of the silent interval between composite sequence and probe melody. The relation between this indirect task measuring the interleaved melody recognition boundary and direct judgments measuring the fission boundary is discussed.

Acoustic Stimulation↗

PubMed2002

The neuroanatomical substrate of sound duration discrimination.

We investigated the neuroanatomical substrate of sound duration discrimination, using the same experimental design as in a previous study on sound intensity discrimination [J. Neurosci. 18 (16) (1998) 6388]. Seven normal subjects were trained to detect deviant sounds presented with a slightly longer duration than a 300 ms long standard harmonic sound, using a Go/No Go paradigm. Individual psychometric curves were assessed using a three-step psychoacoustic procedure. Subjects were then scanned while passively listening to the standard sound, and while discriminating changes in sound duration at four different performance levels (d'=1.5, 2.5, 3.5 and 4.5). Analysis of regional cerebral blood flow (rCBF) data outlined activation, during the discrimination conditions, of a right hemispheric fronto-parietal network very similar to the one previously observed for intensity discrimination, as well as additional activation in the right prefrontal cortex (Brodmann Area (BA) 10), bilateral basal ganglia and cerebellar hemispheres. These findings suggest that discrimination of sound duration, as for discrimination of sound intensity, involves two cerebral networks: a supramodal right fronto-parietal cortical network responsible for allocation of sensory attentional resources, and a network of regions such as the basal ganglia, cerebellum, and right prefrontal cortex, more specifically involved in the temporal aspects of the discrimination task.

Acoustic Stimulation↗

PubMed2002

Schema-based processing in auditory scene analysis.

What is the involvement of what we know in what we perceive? In this article, the contribution of melodic schema-based processes to the perceptual organization of tone sequences is examined. Two unfamiliar six-tone melodies, one of which was interleaved with distractor tones, were presented successively to listeners who were required to decide whether the melodies were identical or different. In one condition, the comparison melody was presented after the mixed sequence: a target melody interleaved with distractor tones. In another condition, it was presented beforehand, so that the listeners had precise knowledge about the melody to be extracted from the mixture. In the latter condition, recognition performance was better and a bias toward same responses was reduced, as compared with the former condition. A third condition, in which the comparison melody presented beforehand was transposed up in frequency, revealed that whereas the performance improvement was explained in part by absolute pitch or frequency priming, relative pitch representation (interval and/or contour structure) may also have played a role. Differences in performance as a function of mean frequency separation between target and distractor sequences, when listeners did or did not have prior knowledge about the target melody, argue for a functional distinction between primitive and schema-based processes in auditory scene analysis.

Adult↗

PubMed1999

Perceptual organization of complex auditory sequences: effect of number of simultaneous subsequences and frequency separation.

Previous findings on streaming are generalized to sequences composed of more than 2 subsequences. A new paradigm identified whether listeners perceive complex sequences as a single unit (integrative listening) or segregate them into 2 (or more) perceptual units (stream segregation). Listeners heard 2 complex sequences, each composed of 1, 2, 3, or 4 subsequences. Their task was to detect a temporal irregularity within 1 subsequence. In Experiment 1, the smallest frequency separation under which listeners were able to focus on 1 subsequence was unaffected by the number of co-occurring subsequences; nonfocused sounds were not perceptually organized into streams. In Experiment 2, detection improved progressively, not abruptly, as the frequency separation between subsequences increased from 0.25 to 6 auditory filters. The authors propose a model of perceptual organization of complex auditory sequences.

Adult↗