A dichotic digit test was administered to 21 subjects with intracranial lesions. Twelve subjects had lesions limited to the cortex and nine had brain stem disorders. The dichotic digit test appeared to be a sensitive measure for detecting cortex and brain stem lesions. Laterality data indicated markedly reduced performance for the ear contralateral to the hemispheric lesion. Overall results were similar to previous reports on dichotic digits, supporting the use of this test as a screening procedure or part of a test battery for CNS evaluation.

Assessment of central auditory dysfunction: the dichotic digit test revisited.

Noise is a pervasive and influential source of stress. Whether through the acute effects of impulse noise or the chronic influence of prolonged exposure, the challenge of noise confronts many who must accomplish vital performance duties in its presence. Although noise has diffuse effects, which are shared in common with many other chronic forms of stress, it also exerts its own specific influences on various forms of cognitive and motor response. We present a quantitative evaluation of these influences so that their harmful effects can be mitigated, their beneficial effects exploited, and any residual effects incorporated and synthesized into selection, training, and design strategies to facilitate human performance capacities. Predictions of single and joint moderator effects were made on the basis of major theories of noise and performance, specifically those explanations based on arousal, masking, or cognitive-resource mechanisms. These predictions were tested through moderator analyses of effects as a function of task type, performance measure, noise type and schedule, and the intensity and duration of exposure. Observed outcome effects (797 effect sizes derived from 242 studies) varied as a function of each of these moderators. Collective findings identified continuous versus intermittent noise, noise type, and type of task as the major distinguishing characteristics that moderated response. Mixed evidence was obtained for the traditional arousal and masking explanations for noise effects. The overall pattern of findings was most consistent with the maximal adaptability theory, a mental-resource-based explanation of stress and performance variation.

Noise Effects on Human Performance: A Meta-Analytic Synthesis

Speech is the primary vehicle of human social interaction. In everyday life, speech communication occurs under an enormous range of different environmental conditions. The demands placed on the process of speech communication are great, but nonetheless it is generally successful. Powerful selection pressures have operated to maximize its effectiveness. The adaptability of speech is illustrated most clearly in its resistance to distortion. In transit from speaker to listener, speech signals are often altered by background noise and other interfering signals, such as reverberation, as well as by imperfections of the frequency or temporal response of the communication channel. Adaptations for robust speech transmission include adjustments in articulation to offset the deleterious effects of noise and interference (Lombard 1911; Lane and Tranel 1971); efficient acousticphonetic coupling, which allows evidence of linguistic units to be conveyed in parallel (Hockett 1955; Liberman et al. 1967; Greenberg 1996; see Diehl and Lindblom, Chapter 3); and specializations of auditory perception and selective attention (Darwin and Carlyon 1995). Speech is a highly efficient and robust medium for conveying information under adverse conditions because it combines strategic forms of redundancy to minimize the loss of information. Coker and Umeda (1974, p. 349) define redundancy as “any characteristic of the language that forces spoken messages to have, on average, more basic elements per message, or more cues per basic element, than the barest minimum [necessary for conveying the linguistic message].” This definition does not address the function of redundancy in speech communication, however. Coker and Umeda note that “redundancy can be used effectively; or it can be squandered on uneven repetition of certain data, leaving other crucial items very vulnerable to noise. . . . But more likely, if a redundancy is a property of a language and has to be learned, then it has a purpose.” Coker and Umeda conclude that the purpose of redundancy in speech communication is to provide a basis for error correction and resistance to noise.

The Perception of Speech Under Adverse Conditions

Objective: To test the accuracy of bilateral language mapping using a standard clinical magnetic resonance (MR) imaging device during word generation. Design. A study of normal volunteers. Setting. Volunteers from the Washington, DC, area. Participants. Nine normal, right-handed, native English speakers (four women, five men, mean age 31 years). Interventions. During four MR acquisition periods, subjects would alternately rest and silently generate words. Sagittal MR images covered the middle and inferior frontal gyri, insulae, and part of the temporal and parietal lobes bilaterally. Main outcome measures. (1) Anatomic maps of task-related signal changes obtained by comparing, in each voxel, the signal during word generation and rest periods, and (2) analysis of the time course of the signal. Results. Maximum responses were in the left hemisphere, mainly in the frontal lobe (Broca9s area, premotor cortex, and dorsolateral prefrontal cortex) but also in posterior regions such as Wernicke9s area. In agreement with previous studies, some degree of task-related changes was present in a subset of the corresponding regions in the right hemisphere. Conclusion. Despite certain limitations, it is possible, using widely available MR equipment, to obtain results consistent with previous studies. The technique may have important implications for assessment of cognitive functions in patients with neurologic disorders in a clinical environment. NEUROLOGY 1995;45: 1821-1827

Functional MRI during word generation, using conventional equipment: A potential tool for language localization in the clinical environment

Both meaningful (sense) and meaningless (nonsense) syllables of the consonant-vowel-consonant type (CVC syllables) and short sentences consisting of 8 or 9 syllables were presented in quiet and in noise to 20 young subjects with normal hearing and to three groups of 20 subjects each with presbycusis, with Meniere's disease and with noise-induced hearing loss. All materials were uttered by a female speaker. The masking noise consisted of continuous noise shaped in accordance with the long-term average spectrum of the speaker. For each individual, the level of the noise was chosen halfway between the speech reception threshold (SRT) for sentences in quiet and 100 dBA. For all groups of subjects in quiet, the SRT for whole-sentence correct scores (sentence SRT) corresponded closely to the SRT for phoneme scores with sense CVC syllables in quiet (CVC phoneme SRT). Averaged across all groups of subjects, sentence SRT in quiet could be predicted within 4.2 dB from CVC phoneme SRT in quiet and sentence SRT in noise within 1.8 dB from CVC phoneme SRT in noise. The prediction error for sentence SRT in quiet using the pure-tone average (PTA) of 0.5, 1 and 2 kHz was 6.0 dB; for sentence SRT in noise using the PTA of 2 and 4 kHz, it was 2.1 dB. In view of the smaller measurement error, a direct measurement of sentence SRT in noise is advisable.

Intelligibility of Dutch CVC Syllables and Sentences for Listeners with Normal Hearing and with Three Types of Hearing Impairment

A new approach to speech audiometry.

A new method for measuring speech‐identification behavior is described. Thirty closed‐message sets were constructed. Each set contained 10 synthetic sentences, representing 4 levels of approximation to a “real” sentence. Sentence length and informational content were controlled. Message identification under conditions of low‐pass filtering and periodic interruption was studied in 30 subjects. Performance varied systematically with informational content. Articulation functions under normal and degraded conditions are compared with analogous functions for more conventional‐speech audiometric materials. [This investigation was supported by National Institute of Neurological Diseases and Blindness, National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.]

Method for Measurement of Speech Identification

An approach to measuring the intelligibility of free-running connected discourse that contrasts with the quasi-statistical methods generally used with nonsense syllables, words, or sentences is des...

Intelligibility of Connected Discourse

Objective:To evaluate relations among scores for phonemes, words in isolation, and words in sentences for listeners with normal hearing and for listeners with sensorineural hearing loss.Design:Ten-word lists of consonant-vowel-consonant monosyllables with each list utilizing the same 10 vowels and 2

Phoneme and word recognition for words in isolation and in sentences

Twenty‐four listeners received 20 dichotic listening runs of 30 pairs of natural CV nonsense syllables per run. Left‐ and right‐ear responses are represented by two partially overlapping normal distributions with equal variance. Observed ear advantages across listening runs are also distributed normally. The means of the distributions of ear advantage are listener specific, but the standard deviations are 10.8%±2.5. The origin of reversals in direction of ear advantage among listening runs is statistical—a small mean/sigma ratio—and approximately six listening runs (180 listening trials) are required to achieve a split‐half reliability coefficient of +0.90.

Charles Speaks

Papers

A new approach to speech audiometry.

Method for Measurement of Speech Identification

Intelligibility of Connected Discourse

Phoneme and word recognition for words in isolation and in sentences

Statistical properties of responses to dichotic listening with CV nonsense syllables.