Recent evidence in natural and semi-natural settings has revealed a variety of left-right perceptual asymmetries among ver- tebrates These include preferential use of the left or right visual hemifield during activities such as searching for food, agonistic re- sponses, or escape from predators in animals as different as fish, amphibians, reptiles, birds, and mammals There are obvious disad- vantages in showing such directional asymmetries because relevant stimuli may be located to the animal's left or right at rando m; there is no a priori association between the meaning of a stimulus (eg, its being a predator or a food item) and its being located to the ani- mal's left or right Moreover, other organisms (eg, predators) could exploit the predictability of behavior that arises from population- level lateral biases It might be argued that lateralization of function enhances cognitive capacity and efficiency of the brain, thus coun- teracting the ecological disadvantages of lateral biases in behavior However, such an increase in brain efficiency could be obtained by each individual being lateralized without any need to align the direction of the asymmetry in the majority of the individuals of the pop- ulation Here we argue that the alignment of the direction of behavioral asymmetries at the population level arises as an "evolutionarily stable strategy" under "social" pressures occurring when individually asymmetrical organisms must coordinate their behavior with the behavior of other asymmetrical organisms of the same or different species

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Survival with an asymmetrical brain: Advantages and disadvantages of cerebral lateralization

In this paper we present evidence supporting the hypothesis that a basic temporal processing impairment in language-impaired children underlies their inability to integrate sensory information that converges in rapid succession in the central nervous system. We provide data showing that this deficit is pansensory; that is, affects processing in multiple sensory modalities, and also affects motor output within the millisecond time frame. We also provide data that links these basic temporal integration deficits to specific patterns of speech perception and speech production deficits in language-impaired children. We suggest that these basic temporal deficits cause a cascade of effects starting with disruption of the normal development of an otherwise effective and efficient phonological system. We propose further that these phonological processing deficits result in subsequent failure to learn to speak and to read normally. That is, both the language and reading problems have their basis in deficiently esta...

Neurobiological Basis of Speech: A Case for the Preeminence of Temporal Processing

The physiological mechanisms and acoustic principles underlying sound production in primates are important for analyzing and synthesizing primate vocalizations, for determining the range of calls that are physically producible, and for understanding primate communication in the broader comparative context of what is known about communication in other vertebrates. In this paper we discuss what is known about vocal production in nonhuman primates, relying heavily on models from speech and musical acoustics. We first describe the role of the lungs and larynx in generating the sound source, and then discuss the effects of the supralaryngeal vocal tract in modifying this source. We conclude that more research is needed to resolve several important questions about the acoustics of primate calls, including the nature of the vocal tract's contribution to call production. Nonetheless, enough is known to explore the implications of call acoustics for the evolution of primate communication. In particular, we discuss how anatomy and physiology may provide constraints resulting in "honest" acoustic indicators of body size. © 1995 Wiley-Liss, Inc.

Vocal production in nonhuman primates: Acoustics, physiology, and functional constraints on “honest” advertisement

Speech perception requires cortical mechanisms capable of analysing and encoding successive spectral (frequency) changes in the acoustic signal. To study temporal speech processing in the human auditory cortex, we recorded intracerebral evoked potentials to syllables in right and left human auditory cortices including Heschl's gyrus (HG), planum temporale (PT) and the posterior part of superior temporal gyrus (area 22). Natural voiced /ba/, /da/, /ga/) and voiceless (/pa/, /ta/, /ka/) syllables, spoken by a native French speaker, were used to study the processing of a specific temporally based acoustico-phonetic feature, the voice onset time (VOT). This acoustic feature is present in nearly all languages, and it is the VOT that provides the basis for the perceptual distinction between voiced and voiceless consonants. The present results show a lateralized processing of acoustic elements of syllables. First, processing of voiced and voiceless syllables is distinct in the left, but not in the right HG and PT. Second, only the evoked potentials in the left HG, and to a lesser extent in PT, reflect a sequential processing of the different components of the syllables. Third, we show that this acoustic temporal processing is not limited to speech sounds but applies also to non-verbal sounds mimicking the temporal structure of the syllable. Fourth, there was no difference between responses to voiced and voiceless syllables in either left or right areas 22. Our data suggest that a single mechanism in the auditory cortex, involved in general (not only speech-specific) temporal processing, may underlie the further processing of verbal (and non-verbal) stimuli. This coding, bilaterally localized in auditory cortex in animals, takes place specifically in the left HG in man. A defect of this mechanism could account for hearing discrimination impairments associated with language disorders.

https://hal.archives-ouvertes.fr/hal-01454129/document

Specialization of Left Auditory Cortex for Speech Perception in Man Depends on Temporal Coding

Lesion studies have indicated that the auditory cortex is crucial for the perception of acoustic space, yet it remains unclear how these neurons participate in this perception. To investigate this,...

Correlation Between the Activity of Single Auditory Cortical Neurons and Sound-Localization Behavior in the Macaque Monkey

Field studies indicate that Japanese macaque (Macaca fuscata) communication signals vary with the social situation in which they occur [S. Green, "Variation of vocal pattern with social situation in the Japanese monkey (Macaca fuscata): A field study," in Primate Behavior, edited by L. A. Rosenblum (Academic, New York, 1975), Vol. 4]. A significant acoustic property of the contact calls produced by these primates is the temporal position of a frequency peak within the vocalization, that is, an inflection from rising to falling frequency [May et al., "Significant features of Japanese macaque communication sounds: A psychophysical study," Anim. Behav. 36, 1432-1444 (1988)]. The experiments reported here are based on the hypothesis that Japanese macaques derive meaning from this temporally graded feature by parceling the acoustic variation inherent in natural contact calls into two functional categories, and thus exhibit behavior that is analogous to the categorical perception of speech sounds by humans. To test this hypothesis, Japanese macaques were trained to classify natural contact calls by performing operant responses that signified either an early or late frequency peak position. Then, the subjects were tested in a series of experiments that required them to generalize this behavior to synthetic calls representing a continuum of peak positions. Demonstration of the classical perceptual effects noted for human listeners suggests that categorical perception reflects a principle of auditory information processing that influences the perception of sounds in the communication systems not only of humans, but of animals as well.

Categorical perception of conspecific communication sounds by Japanese macaques, Macaca fuscata

The significant features of Japanese macaque coo sounds: a psychophysical study

Directional hearing acuity, as measured by the minimum audible angle (MAA), was determined in four Old World monkeys, Macaca radiata. The acoustic stimuli were linear changes in frequency (sweeps) for different frequency ranges and sweep rates. The sweeps ranged between 0.5 and 1.3 kHz, at two durations, 100 and 200 ms. In upsweeps which began at 0.5 kHz and were 200 ms in duration, MAA decreased as sweep rate and frequency range increased. These thresholds were compared to MAAs of sweeps which traversed the same range of frequencies but at a different rate, to MAAs of sweeps with identical rates but over different frequency ranges, and to the MAAs of downsweeps. These comparisons indicated that range, and not sweep rate, exerts the greatest effect on the MAA. Interaural phase differences derived from the upper limits of the frequency range are discussed as potential FM localization cues.

Sound localization of frequency‐modulated sinusoids by Old World monkeys

The directional dependence of the transfer function from free‐field plane waves to a point near the tympanic membrane was measured in anesthetized domestic cats. A probe tube microphone was placed from a ventral approach, which minimally affects the head and pinae. Acoustic measurements were taken using a quasianechoic method in which an impulsive stimulus was presented and room reflections were rejected using a Kaiser window. The transfer functions are similar to those reported earlier [A.D. Musicant et al., 12th ICA, Toronto (July 1986)]. They can be broken into three distinct frequency ranges: A low‐frequency range ( 18 kHz), where the spectrum varies greatly with source location. The frequency of the midfrequency notch is a robust cue for sound source direction; it varies with both azimuth and elevation in a monotonic fashion in the frontal field. Source direction is uniquely determined by combining the midfrequency notch cue from both ears. These results suggest that simple consideration of interaural level differences may not be sufficient for the study of sound localization at high frequencies. [Work supported by Grant No. NS12524 from NINCDS/NIDCD.]

Brad May

Papers

Categorical perception of conspecific communication sounds by Japanese macaques, Macaca fuscata

The significant features of Japanese macaque coo sounds: a psychophysical study

Sound localization of frequency‐modulated sinusoids by Old World monkeys

Directional dependence of free‐field‐to‐eardum transformations in cats