Mathematical treatment of context effects in phoneme and word recognition

Abstract

Percent recognition of phonemes and whole syllables, measured in both consonant-vowel-consonant (CVC) words and CVC nonsense syllables, is reported for normal young adults listening at four signal-to-noise (S/N) ratios. Similar data are reported for the recognition of words and whole sentences in three types of sentence: high predictability (HP) sentences, with both semantic and syntactic constraints; low predictability (LP) sentences, with primarily syntactic constraints; and zero predictability (ZP) sentences, with neither semantic nor syntactic constraints. The probability of recognition of speech units in context (pc) is shown to be related to the probability of recognition without context (pi) by the equation pc = 1 - (1-pi)k, where k is a constant. The factor k is interpreted as the amount by which the channels of statistically independent information are effectively multiplied when contextual constraints are added. Empirical values of k are approximately 1.3 and 2.7 for word and sentence context, respectively. In a second analysis, the probability of recognition of wholes (pw) is shown to be related to the probability of recognition of the constituent parts (pp) by the equation pw = pjp, where j represents the effective number of statistically independent parts within a whole. The empirically determined mean values of j for nonsense materials are not significantly different from the number of parts in a whole, as predicted by the underlying theory. In CVC words, the value of j is constant at approximately 2.5. In the four-word HP sentences, it falls from approximately 2.5 to approximately 1.6 as the inherent recognition probability for words falls from 100% to 0%, demonstrating an increasing tendency to perceive HP sentences either as wholes, or not at all, as S/N ratio deteriorates.

Development of a Danish speech intelligibility test

“…The j-factor is likely to vary between different sentences, and may even vary for the same sentence, depending on the SNR (Boothroyd & Nittrouer, 1988). In a sentence with j 01.5 and a WI of 70% evenly distributed between all words, the SI will be 59% (0.7 1.5 00.59).…”

“…Boothroyd & Nittrouer (1988) introduced the j-factor, which is equal to the number of independently recognized parts in a sentence. Each part will consist of one or more words.…”

“…Each part will consist of one or more words. In a normal, conversational five-word sentence, j will be in the order of two to three (Boothroyd & Nittrouer, 1988). The intelligibility of a sentence can be calculated as the product of the part intelligibilities.…”

Consonant recognition loss in hearing impaired listeners

“…A context effect due to meaning, grammar, prosody, etc., increases the recognition scores in noisy conditions without actually improving the perception of speech sounds ͑French and Steinberg, 1947;Boothroyd and Nittrouer, 1988͒. The effect of context information on the ⌬SNR 50 metric has not been measured.…”

Cochlea-scaled entropy, not consonants, vowels, or time, best predicts speech intelligibility

“…Instead, sentences provide numerous linguistic cues (syntax, semantics, prosody, etc. ), so understanding one word in a sentence greatly increases predictability of adjacent words (35,36). Consequently, a little more acoustics can serve to engage predictability at higher levels in distinctly nonlinear ways.…”