Semantic Predictability Facilitates Comprehension of Degraded Speech in a Graded Manner.

Pratik Bhandari,Jutta Kray,Vera Demberg

doi:10.3389/fpsyg.2021.714485

Abstract

Previous studies have shown that at moderate levels of spectral degradation, semantic predictability facilitates language comprehension. It is argued that when speech is degraded, listeners have narrowed expectations about the sentence endings; i.e., semantic prediction may be limited to only most highly predictable sentence completions. The main objectives of this study were to (i) examine whether listeners form narrowed expectations or whether they form predictions across a wide range of probable sentence endings, (ii) assess whether the facilitatory effect of semantic predictability is modulated by perceptual adaptation to degraded speech, and (iii) use and establish a sensitive metric for the measurement of language comprehension. For this, we created 360 German Subject-Verb-Object sentences that varied in semantic predictability of a sentence-final target word in a graded manner (high, medium, and low) and levels of spectral degradation (1, 4, 6, and 8 channels noise-vocoding). These sentences were presented auditorily to two groups: One group (n =48) performed a listening task in an unpredictable channel context in which the degraded speech levels were randomized, while the other group (n =50) performed the task in a predictable channel context in which the degraded speech levels were blocked. The results showed that at 4 channels noise-vocoding, response accuracy was higher in high-predictability sentences than in the medium-predictability sentences, which in turn was higher than in the low-predictability sentences. This suggests that, in contrast to the narrowed expectations view, comprehension of moderately degraded speech, ranging from low- to high- including medium-predictability sentences, is facilitated in a graded manner; listeners probabilistically preactivate upcoming words from a wide range of semantic space, not limiting only to highly probable sentence endings. Additionally, in both channel contexts, we did not observe learning effects; i.e., response accuracy did not increase over the course of experiment, and response accuracy was higher in the predictable than in the unpredictable channel context. We speculate from these observations that when there is no trial-by-trial variation of the levels of speech degradation, listeners adapt to speech quality at a long timescale; however, when there is a trial-by-trial variation of the high-level semantic feature (e.g., sentence predictability), listeners do not adapt to low-level perceptual property (e.g., speech quality) at a short timescale.

Highlights

Understanding speech is highly automatized and seemingly easy when conditions are optimal
The goals of the present study were threefold: First, to examine the interplay between perceptual and cognitive processing during language comprehension to answer the question whether the predictability of the sentence context facilitates language comprehension in a graded manner primarily when the speech signal is distorted, second, to assess whether perceptual adaptation influences the interplay between perceptual and language processing, and third, to establish a sensitive metric that takes into account the use of context in language comprehension
There was a main effect of target word predictability, suggesting that response accuracy was lower at low predictability than both high-predictability [β = 2.18, SE = 0.30, z (6917) = 7.21, p < 0.001] and medium-predictability sentences [β = −0.52, SE = 0.27, z (6917) = −1.97, p = 0.049]

Summary

Introduction

Understanding speech is highly automatized and seemingly easy when conditions are optimal. Ambient noise is an environmental factor that distorts the speech signal and renders it difficult to understand. The noise coming from people talking in the background might make it difficult for you to understand what your friend is saying, while you are chatting in a café. A conversation with a friend over the phone can be corrupted by a poor transmission of the speech signal which in turn hampers language comprehension. The speech signal is sometimes bad or the environment is noisy, listeners do not always fail to understand what a friend is saying in the café or over the phone. Listeners are successful in understanding distorted speech by utilizing context information which contains information in a given situation about a topic of conversation, semantic and syntactic information of a sentence structure, world knowledge, visual information, etc. The goals of the present study were threefold: First, to examine the interplay between perceptual and cognitive processing during language comprehension to answer the question whether the predictability of the sentence context facilitates language comprehension in a graded manner primarily when the speech signal is distorted, second, to assess whether perceptual adaptation influences the interplay between perceptual and language processing, and third, to establish a sensitive metric that takes into account the use of context in language comprehension

Objectives

Methods

Results

Conclusion