Estimation of sensory information transmission using a hidden Markov model of speech stimuli
Arne Leijon · Acta acustica united with Acustica · 2002
A method is presented which gives good approximate estimates of the rate. of information (in bits/s) successfully transmitted from a speech source to the modelled neural output of the peripheral sensory system. This information rate sets definite upper limits on the listener's speech-recognition performance. The performance limits depend on the entropy and vocabulary size of the speech material. The estimates of sensory information rate can be used to evaluate to what extent a listeners' performance is limited by peripheral loss of information or by suboptimal central processing. Calculations for a Swedish sentence test material, with an excitation-pattern auditory model, were consistent with human speech recognition results in speech-shaped masking noise. This suggests that the scarcity of sensory information may be the primary limiting factor in this test condition. Similar calculations for low-pass- and high-pass-filtered clean speech indicated a higher sensory information rate than required for the listeners' actual performance. These results suggest that the speech recognition performance under masking and filtering may be limited by different mechanisms. The analysis also showed that the information in adjacent frequency bands is not additive.