Biomedical subjects

Christopher J Darwin

Publications and source records attributed to Christopher J Darwin.

4 recordsLinked to original sources

PubMed2006

Contributions of binaural information to the separation of different sound sources.

Binaural hearing aids potentially provide binaural cues that can improve the dectability and the spatial separation of multiple sound sources. This paper considers the use of binaural cues and the resultant spatial percepts on listeners' ability to separate simultaneous sound sources. In backgrounds with continuous noise or multiple talkers, the main problem is the detection of individual acoustic components. On the other hand, if a single masking sound is very similar to the target, and both target and masker are spectro-temporally sparse, as is the case with speech, the main problem, at least for listeners with normal hearing, is to decide whether a particular spectro-temporal feature belongs to the target source and to track that source across time. Although the subjective location of a sound source can help in grouping features across time, its effect is most easily observed in the absence of other differences between the sound sources.

Environment↗

PubMed2006

Processing unattended speech.

Three experiments examine the effect of a difference in fundamental frequency (F0) range between two simultaneous voices on the processing of unattended speech. Previous experiments have only found evidence for the processing of nominally unattended speech when it has consisted of isolated words which could have attracted the listener's attention. A paradigm recently used by Dupoux et al. [J. Exp. Psychol.: Human Percept. Perform. 29(1), 172-184 (2003)] was modified so that participants had to detect a target word belonging to a specific category presented in a rapid list of words in the attended ear. In the unattended ear, concatenated sentences were presented, some containing a repetition prime presented just before a target word. Primes speeded category detection by 25 ms when the two messages were in a difference F0 range. This priming effect was unaffected by whether the target was led to the left or the right ear, but disappeared when there was no F0 range difference between the messages. Finally, it was replicated when participants were compelled to focus on the attended message in order to perform a second task. The results demonstrate that repetition priming can be produced by words in unattended continuous speech provided that there is a difference in F0 range between the voices.

Acoustic Stimulation↗

PubMed2005

Across-ear interference from parametrically degraded synthetic speech signals in a dichotic cocktail-party listening task.

Recent results have shown that listeners attending to the quieter of two speech signals in one ear (the target ear) are highly susceptible to interference from normal or time-reversed speech signals presented in the unattended ear. However, speech-shaped noise signals have little impact on the segregation of speech in the opposite ear. This suggests that there is a fundamental difference between the across-ear interference effects of speech and nonspeech signals. In this experiment, the intelligibility and contralateral-ear masking characteristics of three synthetic speech signals with parametrically adjustable speech-like properties were examined: (1) a modulated noise-band (MNB) speech signal composed of fixed-frequency bands of envelope-modulated noise; (2) a modulated sine-band (MSB) speech signal composed of fixed-frequency amplitude-modulated sinewaves; and (3) a "sinewave speech" signal composed of sine waves tracking the first four formants of speech. In all three cases, a systematic decrease in performance in the two-talker target-ear listening task was found as the number of bands in the contralateral speech-like masker increased. These results suggest that speech-like fluctuations in the spectral envelope of a signal play an important role in determining the amount of across-ear interference that a signal will produce in a dichotic cocktail-party listening task.

Adult↗

PubMed2003

Effects of fundamental frequency and vocal-tract length changes on attention to one of two simultaneous talkers.

Three experiments used the Coordinated Response Measure task to examine the roles that differences in F0 and differences in vocal-tract length have on the ability to attend to one of two simultaneous speech signals. The first experiment asked how increases in the natural F0 difference between two sentences (originally spoken by the same talker) affected listeners' ability to attend to one of the sentences. The second experiment used differences in vocal-tract length, and the third used both F0 and vocal-tract length differences. Differences in F0 greater than 2 semitones produced systematic improvements in performance. Differences in vocal-tract length produced systematic improvements in performance when the ratio of lengths was 1.08 or greater, particularly when the shorter vocal tract belonged to the target talker. Neither of these manipulations produced improvements in performance as great as those produced by a different-sex talker. Systematic changes in both F0 and vocal-tract length that simulated an incremental shift in gender produced substantially larger improvements in performance than did differences in F0 or vocal-tract length alone. In general, shifting one of two utterances spoken by a female voice towards a male voice produces a greater improvement in performance than shifting male towards female. The increase in performance varied with the intonation patterns of individual talkers, being smallest for those talkers who showed most variability in their intonation patterns between different utterances.

Attention↗