Effects of eye movements on the recognition and localization of dichotic stimuli

Three experiments examined the effect of gaze shifts on overall performance and ear differences in dichotic listening. In the first two experiments, lights were switched on and off so as to induce rightward, leftward, or upward gaze during dichotic stimulation. The dichotic material consisted of musical passages in Experiment 1 and two kinds of verbal material in Experiment 2. Vertical eye movements enhanced the accuracy of identification of music but not verbal material. The lateral direction of eye movements affected subjects' ability to localize targets in Experiment 1: localization was more accurate in the direction toward which subjects were looking. In the third experiment it was found that optokinetic nystagmus (OKN) influenced the asymmetry of performance on a dichotic consonant-vowel (CV) test. The right-ear advantage was greatest when the OKN drum rotated from left to right and least when it rotated from right to left. The effect was due to corresponding variation in left-ear scores. Possible mechanisms through which shifts of gaze affect auditory identification and localization are proposed.

Proprioceptive influences on auditory and visual spatial localization

We evaluated the influence of proprioceptive information about arm position on the perceptual localization of auditory and visual targets attached to the hand. Our approach was to distort the perceived position of the restrained arm by means of mechanical vibration of the biceps brachii muscle; such vibration elicits compelling apparent extension of the stationary forearm (Goodwin, G. M., D. I. McCloskey, and P. B. C. Matthews (1972) Science 175: 1382-1384, Brain 95: 705-748), and subjects report changes in the apparent directions of the auditory and visual targets attached to their hand. These changes are in the same direction and plane as apparent arm motion and their onsets are coincident with or lag slightly behind the experienced displacement of the arm. While visual motion is being experienced, a subject's eyes remain steadily fixating the target light. The pattern of findings demonstrates that proprioceptive information about limb position can influence the central representation of gaze and auditory localization can be similarly influenced. The biasing of auditory localization indicates that identical patterns of arrival time and intensity cues at the two ears can give rise to the perception of sounds in widely disparate spatial positions in relation to the head and body, depending on the proprioceptive representation of the direction of the sound source.

Auditory attentional abilities in hyperactive children

Using dichotic monitoring procedures, various aspects of auditory attention were examined in hyperactive children and matched normal controls. Hyperactive children did not show deficits in the ability to sustain attention, although signal detection analysis showed some lowered capacity in both focused and selective attention to targets. Subsamples of learning-disabled and neurologically impaired hyperactive children showed minimal impairment of auditory attentional capacities. It was argued that more evidence concerning task and situational effects is needed before it can be claimed that hyperactive children show attention deficits.

Brainstem auditory-evoked responses and clinical picture in a one year follow-up of 18 patients with Friedreich ataxia

Brainstem auditory-evoked responses (BAER) and behavior audiometry were evaluated on 18 patients with Friedreich ataxia. Behavior audiometry showed a normal pure tone test, normal performance intensity and phonetically balanced functions in all patients. BAER were abnormal in all patients. The data obtained show a good correlation between BAER and clinical picture and suggest that BAER could be useful in monitoring the clinical condition of FA patients.

Self-report of the frequency and phenomenology of verbal hallucinations

This study was an assessment of several parameters of verbal hallucinations ("voices") based on the self-report of 52 hallucinating psychiatric patients. These subjects were asked to estimate the frequency of their hallucinations and to rate phenomenological aspects (loudness, clarity, location, reality) of their most recent hallucination. Each parameter was assessed with two visual analogue scales which differed in their wording of the dimension. Results showed that the reliability of the subjects' estimates on the parameters differed greatly. Clarity was most reliably reported and reality was least reliably reported. Historical notions that schizophrenics characteristically perceive external "voices" and that such "voices" are perceived as more real were not supported. There was a significant negative correlation between the perceived location and the perceived clarity of hallucinations. No significant differences in mean parameter scores were found between two groups of subjects, schizophrenics and affective psychotics.

Central presbycusis

The phenomenon of central presbycusis has been investigated employing a central auditory battery in elderly individuals with essentially normal hearing. The studies indicate a progressive loss in central auditory competence measured by simultaneous binaural challenges and frequency and temporal distortion tests. The rate of failure is related to age, on the whole, but there is increasing variability from the normals with seniority. The hearing disability in noise or speech competitive environments is explained by these data. Auditory disabilities related to poor articulation and rapid speech presentation are identified by other tests in the battery. Central presbycusis, in addition to the peripheral form, does exist and further compounds the hearing disorder in many elderly.

Lateral-position-based models of interaural discrimination

This letter investigates the hypothesis that lateral position is the only cue available for interaural discrimination experiments using 500-Hz stimuli. The discussion of this hypothesis is in the context of comparisons of the experimental data to predictions of the "position-variable" model of binaural interaction. The model predicts the mean and variance of the subjective lateral position of stimuli used in the discrimination experiments, assuming that discrimination performance is based on optimal processing of this subjective position. To the extent that the laterality predictions of the model are accurate, data that are inconsistent with its predictions would also be problematical for any model based on the subjective laterality of a single binaural image. The predictions (at least qualitatively) describe much of the observed experimental data, including a number of results that have not been addressed by any previous theory. Nevertheless, the observed performance is significantly better than the corresponding predictions for three types of experiments in which the utility of the position cue has been eliminated by experimental design. We believe that our results indicate that changes in lateral position are the primary cue in most interaural discrimination experiments, but that secondary attributes of the perceptual images can be useful when performance based on position alone would be poor.

Spectral sharpness and vowel dissimilarity

The effect of sharpening or smoothing the spectral envelopes of synthetic vowel-like sounds on the dissimilarities perceived among these sounds was investigated by means of triadic comparisons. When a spectral envelope (dB on a log-frequency scale) is considered the sum of a series of sinusoidal spectral modulations (or ripples) of different densities (the ripple spectrum), spectral sharpening or smoothing can be described as an amplification or attenuation of a part of the original ripple spectrum. For a set of nine sounds comprising different degrees of spectral sharpening of a single vowel, the perceived dissimilarities were found to be dominated by a specific part of the ripple spectrum, i.e., by spectral modulations with a density of about 2 ripples/oct. The possible role of lateral suppression in relation to this dominant region is discussed. For a set of 18 sounds comprising six vowels, each in three different versions (sharpened, normal, or smoothed), the dissimilarities were found to be determined mainly by the global shape of the spectral envelopes, i.e., by spectral modulations up to about 1.5-2 ripples/oct. Details of the spectral envelope (including the region of 2 ripples/oct where lateral suppression is effective) appear to be of minor influence on vowel dissimilarities.

Acquiring language through total communication

Total communication provides an opportunity for very young children to receive training through both visual and auditory systems. Most children with severe hearing loss have auditory discrimination/perceptual problems in addition to a loss of hearing sensitivity. Because sophisticated assessment of auditory perceptual problems is not yet possible in hearing impaired infants, total communication provides immediate and consistent language input regardless of eventual determination of auditory perceptual skills. An illustration of a total communication program is provided.

Influence of monaural spectral cues on binaural localization

Seven subjects located, monaurally and binaurally, narrow bands of noise originating in the horizontal plane. The stimuli were 1.0 kHz wide and centered at 4.0-14.0 kHz in steps of 0.5 kHz. The loudspeakers, 15 deg apart, were arranged in a semicircle (0-270-180 deg, azimuth). In the first part of the experiment all sounds emanated from the loudspeaker at 270 deg, but their apparent locations varied widely as a function of their center frequency. For each subject, the pattern of location judgments under the binaural listening condition corresponded to that recorded for the monaural condition. In the second part of the experiment the loudspeaker from which each of the same narrow bands of noise emanated was varied in irregular order. Again, monaural location judgments were governed by the frequency content of the noise bands. Binaural location judgments were strongly influenced by the sounds' frequency composition when the stimuli originated from 315-225 deg, notwithstanding the presence of interaural differences in time and intensity. For narrow bands of noise emanating off midline, monaural spectral cues significantly override binaural difference cues, and they also determine the resolution of front-back ambiguities.

[Tachistophony, a measuring method for time threshold in hearing. A contribution to hearing theory]

Tachistophony is presented as a method of measuring time-thresholds for understanding spoken signals and for recognising sound levels. The minimum total-time of periodically interrupted sound-events per second is assessed. The pause-total can reach a value between 4 and 9 times (in extreme cases up to 14 times) the sound flow period. The total of sound-pulses is measured only at 250 to 100 ms, with the recognition of values still operative. Due to the low information-content of numerical words their time-threshold is the lowest. The time-threshold lies considerably higher for one-syllable words and sentences with a higher information-content. The superiority of the left ear with dichotic stimulation is confirmed with monaural tachistophonic stimulation. These values are related to phase-frequencies of between 13 and 40 Hz. When the phase-frequency is lowered, comprehension below 8 Hz falls considerably. This is less apparent with phase-frequencies between 40 and 110 Hz.

Rhythms and responses

Rhythms are fundamental to behavior, but the control mechanism for timed responses is not known. Many theorists have assumed that there is a central clock coordinating behavior in all sensory modalities and response modes. We tested this hypothesis using a rhythmic tapping task in which university undergraduates first attempted to synchronize responses with brief auditory, tactile, or visual stimuli and then continued to tap at the same rate on their own. Performance was most variable with visual stimuli and least variable with auditory stimuli. The detailed results suggest that performances are not based on a common clock, but, rather, different strategies are employed when the task is presented in different modalities. We reject the hypothesis of a single timing mechanism as controlling behavior and, in doing so, question the validity of information processing models that are formulated without regard to temporal relations among their conjectured processes.

Development of visually controlled maternal preferences in Peking ducklings

The interaction between natural visual and auditory stimulation in the control of filial behavior was studied in domestic mallard (Peking) ducklings during the first 3 days of postnatal life. Visual imprinting at 24 hr resulted in a visual preference for the familiar model over an unfamiliar model in each of two choice tests, one at 48 hr and one at 72 hr, but only if both models were silent. If both models emitted a recording of the mallard maternal call, the visual preference was found only in the later (72-hr) test. Visuomotor experience between training and testing was found to be essential for the development of the visual preference at 72 hr, but the required experience was of a very general nature. Either a choice test with silent models or a period of social rearing (between 24 and 72 hr) provided effective experience. Thus, the ability to show a visual preference in the presence of the maternal call at 72 hr depends on experience, but not necessarily on further exposure to the imprinting object or to any specific aspects of the test situation. These results demonstrate the importance of normal visual, motor and/or social experience to the development of the visual control of filial behavior in ducklings.

The four factors leading to binaural masking-level differences

A simple extension of the Webster-Jeffress model is presented together with its predictions for the effects of various stimulus parameters on the size of binaural masking-level differences (BMLDs). The four factors leading to BMLDs (just-noticeable differences (JNDs), temporal effects in simultaneous masking, binaural interaction, and temporal effects in non-simultaneous masking) are described, new measurements of the effect of signal duration on the detectability of interaural delay are presented, and the high degree of correlation between observers' sensitivity to changes in level and their sensitivity to changes in interaural delay is demonstrated. A number of examples illustrating where knowledge of JNDs for level and interaural delay and their joint dependence on certain stimulus parameters are sufficient to predict BMLDs are discussed.

The binaural masking level difference as a function of frequency, masker level and masking bandwidth in normal-hearing and hearing-impaired listeners

Binaural masking level differences (MLDs) were measured for 10 normal-hearing and 10 cochlear-impaired listeners, at 500 and 2 000 Hz. Maskers were either wide-band (approximately 2 000 Hz), or narrow-band (50 Hz). For wide-band maskers the noise pressure spectrum level was 50 dB/Hz, and for the narrow-band maskers the noise levels were 50 and 60 dB/Hz. At 500 Hz the hearing-impaired listeners show abnormally low MLDs in wide-band noise, but not in narrow-band noise. At 2 000 Hz, the hearing-impaired subjects show abnormally low MLDs only in narrow-band noise at the 50 dB/Hz level. The clinical implications of the results are considered.

Cognition and symptomatology in schizophrenia

The experimental work on cognitive processes in schizophrenia is critically reviewed with respect to its relevance in understanding schizophrenic symptomatology. Several logical and empirical issues that complicate any comprehensive attempt to relate schizophrenic symptoms and information processing are discussed. Studies germane to schizophrenic sensory/perceptual, cognitive, affective, and motor anomalies are examined, and it is concluded that the cognitive approach to these areas is promising, but further research and theory elaboration will be required in order to provide a firm basis for cognitively oriented intervention attempts.

[Directionality of sound perception in the external ear of the dog]

Sound pressure level of tone was measured using a probe tube microphone at entrance to the dog's external meatus as a function of the azimuth of the sound source. It was demonstrated that directionality of the dog's external ear and corresponding values of interaural intensity differences (delta I) were gradually increased as the tone frequency raised from 0.5 to 40 kHz. Transfer in pinnae locations from lateral to frontal positions (one of the components of orientation reaction to an unexpected sound) resulted in some narrowing of directionality diagrams and in a displacement of their maxima towards the head midline. It was calculated that owing to this effects the extent of monotonic part of the function relating delta I and azimuth of a source were enlarged. The lateral pinnae position was suggested to be optimal for sound detection and the frontal one for localization of the moving sound source.

Sound localization in wild Norway rats (Rattus norvegicus)

The ability of three wild Norway rats to localize sound was determined for single clicks and 100-ms white noise bursts. Chance level localization thresholds were 12 degrees for clicks and 9.7 degrees for white noise. A comparison of these results with published localization thresholds for the domestic albino rat yielded no significant differences. It appears that the combined effects of domestication and albinism have not affected the ability of the laboratory rat to localize sound. Instead, the relatively poor localization acuity of these rats appears to be part of the normal variation in sound localization acuity found among different species of mammals.

Speechreading supplemented with formant-frequency information from voiced speech

The benefit of supplementing speechreading with information about the frequencies of the first and second formants from the voiced sections of the speech signal was studied by presenting short sentences to 18 normal-hearing listeners under the following three conditions: (a) speechreading combined with listening to the formant-frequency information, (b) speechreading only, and (c) formant-frequency information only. The formant frequencies were presented either as pure tones or as a complex speechlike signal, obtained by filtering a periodic pulse sequence of 250 Hz by a cascade of four second-order bandpass filters (with constant bandwidth); the center frequencies of two of these filters followed the frequencies of the first and second formants, whereas the frequencies of the others remained constant. The percentage of correctly identified syllables increased from 22.8 in the case of speechreading only to 82.0 in the case of speechreading while listening to the complex speechlike signal. Listening to the formant information only scored 33.2% correct. However, comparison with the best-scoring condition of our previous study [Breeuwer and Plomp, J. Acoust. Soc. Am. 76, 686-691 (1984)] indicates that information about the sound-pressure levels in two one-octave filter bands with center frequencies of 500 and 3160 Hz is a more effective supplement to speechreading than the formant-frequency information.

Localization of pure tones and click trains by untrained humans

Minimum audible angles (m.a.a.s) of untrained subjects were measured in a room using pure tone (0.5 to 8 kHz) and click train (noise) stimuli (two alternative, forced-choice, constant stimulus with feedback and head movements permitted, horizontal plane, 0 degree azimuth). The m.a.a.s and standard deviations (SD) were 3.0 degrees +/- 5.2 degrees for click trains and 10.9 degrees +/- 21.0 degrees for pure tones. The m.a.a.s did not vary significantly with frequency. The m.a.a.s and their SDs matched values reported from localization error studies. Narrowing the testing range from 32 degrees to 8 degrees resulted in random responses to the pure tones, though the click trains were readily localized. One subject presented with 2500 trials using an 8 kHz pure tone (with feedback, 16 degrees range) increased her responses from random to 88% correct during the testing. The click train m.a.a.s probably reflect the typical noise localizational abilities of the general population. For pure-tone m.a.a.s, experience/training may result in improved accuracy not applicable to the general public. The presence of a well defined time clue and a broad bandwidth sound results in significantly lower m.a.a.s than were obtained using pure tones which presumably present only interaural phase or intensity clues.