Probe-Signal Investigation of an Attentional Filter for Fundamental Frequency
Degree GrantorUniversity of Canterbury
Degree NameMaster of Audiology
When listeners are detecting tones of a given frequency in noise, they operate with a narrowband attentional filter which is tuned to the frequency of the attended tone. This means that tones with frequencies which match that which is being attended to, will be detected, whereas tones with frequencies outside the filter will be detected at chance levels. In the current study, attentional filters were measured on two auditory dimensions. The first experiment employed a modified version of the methods of previous studies to measure attentional filters in the frequency dimension (Greenberg & Larkin, 1968). The mean results replicated those of previous experiments, revealing an attentional filter for frequency. In the second experiment, the methods of the first experiment were used to investigate whether there is an attentional filter in the fundamental frequency (f0) dimension. To test this, sentences with a given f0 were presented in noise. Infrequently, sentences were presented with f0s which the listeners were not attending to. The changes in f0 (∆f0) tested were ± 5 Hz and ±10 Hz, with respect to the expected 220 Hz f0. The effect of ∆f0 was investigated using sentence identification scores. Mean results indicated that listeners were best at identifying the sentences with an expected f0, and sentences with ∆f0s of 10 Hz from the expected f0. Sentences with ∆f0s of 5 Hz from the expected f0, on the other hand, were more poorly detected. This could be due to the presence of an attentional filter for f0, which has a narrow bandwidth, ranging between 10 and 20 Hz. An attentional filter for f0 may have different properties than those for attentional filters for frequency. The complex nature of sentence materials might change the way that attention is allocated across the f0 distribution, so that greater changes in f0 may be enough to switch the listeners’ attention to that f0. Overall, the results did not approximate the typical attentional filter shape which was found for frequency. Therefore, the results cannot be used to demonstrate the existence of attentional filters for f0. The presence of an attentional filter for f0, however, cannot be ruled out. Further research is needed, using a greater variety of ∆f0s to confirm and further investigate the presence, and properties of an attentional filter for f0.