The concept of auditory stimulus representation in cognitive neuroscience.

The sequence of neurophysiological processes elicited in the auditory system by a sound is analyzed in search of the stage at which the processes carrying sensory information cross the borderline beyond which they directly underlie sound perception. Neurophysiological data suggest that this transition occurs when the sensory input is mapped onto the physiological basis of sensory memory in the auditory cortex. At this point, the sensory information carried by the stimulus-elicited process corresponds, for the first time, to that contained by the actual sound percept. Before this stage, the sensory stimulus code is fragmentary, lacks the time dimension, cannot enter conscious perception, and is not accessible to top-down processes (voluntary mental operations). On these grounds, 2 distinct stages of auditory sensory processing, prerepresentational and representational, can be distinguished. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The functional anatomy of sound intensity discrimination

The human neuroanatomical substrate of sound intensity discrimination was investigated by combining psychoacoustics and functional neuroimaging. Seven normal subjects were trained to detect deviant sounds presented with a slightly higher intensity than a standard harmonic sound, using a Go/No Go paradigm. Individual psychometric curves were carefully assessed using a three-step psychoacoustic procedure. Subjects were scanned while passively listening to the standard sound and while discriminating changes in sound intensity at four different performance levels (d' = 1.5, 2.5, 3.5, and 4.5). Analysis of regional cerebral blood flow data outlined activation, during the discrimination conditions, of a right hemispheric frontoparietal network already reported in other studies of selective or sustained attention to sensory input, and in which activity appeared inversely proportional to intensity discriminability. Conversely, a right posterior temporal region included in secondary auditory cortex was activated during discrimination of sound intensity independently of performance level. These findings suggest that discrimination of sound intensity involves two different cortical networks: a supramodal right frontoparietal network responsible for allocation of sensory attentional resources, and a region of secondary auditory cortex specifically involved in sensory computation of sound intensity differences.     

Transient "deafness" accompanies auditory development during metamorphosis from tadpole to frog

During metamorphosis, ranid frogs shift from a purely aquatic to a partly terrestrial lifestyle. The central auditory system undergoes functional and neuroanatomical reorganization in parallel with the development of new sound conduction pathways adapted for the detection of airborne sounds. Neural responses to sounds can be recorded from the auditory midbrain of tadpoles shortly after hatching, with higher rates of synchronous neural activity and lower sharpness of tuning than observed in postmetamorphic animals. Shortly before the onset of metamorphic climax, there is a brief "deaf" period during which no auditory activity can be evoked from the midbrain, and a loss of connectivity is observed between medullary and midbrain auditory nuclei. During the final stages of metamorphic development, auditory function and neural connectivity are restored. The acoustic communication system of the adult frog emerges from these periods of anatomical and physiological plasticity during metamorphosis.     

The cognitive and neural correlates of tactile memory.

Tactile memory systems are involved in the storage and retrieval of information about stimuli that impinge on the body surface and objects that people explore haptically. Here, the authors review the behavioral, neuropsychological, neurophysiological, and neuroimaging research on tactile memory. This body of research reveals that tactile memory can be subdivided into a number of functionally distinct neurocognitive subsystems, just as is the case with auditory and visual memory. Some of these subsystems are peripheral and short lasting and others are more central and long lasting. The authors highlight evidence showing that the representation of tactile information interacts with information about other sensory attributes (e.g., visual, auditory, and kinaesthetic) of objects/events that people perceive. This fact suggests that at least part of the neural network involved in the memory for touch might be shared among different sensory modalities. In particular, multisensory/amodal information-processing networks seem to play a leading role in the storage of tactile information in the brain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory prerequisites of mismatch negativity in the auditory event-related potential (ERP).

The mismatch negativity (MMN) is a component of the auditory event-related brain potential that occurs in response to infrequent changes in the physical properties of homogeneous series of sounds, even when Ss are instructed to ignore the auditory channel of stimulation. It has been proposed (e.g., R. N??t?nen, see record 1991-00298-001) that the MMN is generated by an automatic process in which a difference between the deviant sound and the previous, standard sound is detected by the brain. However, it is unclear how the form of memory involved is related to the rest of the memory system. The present study indicates that, for an MMN to be elicited in response to a change in tone frequency, the representation of the standard tone must be both well-established as a standard in memory and in a currently active state. The relation between physiological and psychological aspects of memory representation is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Physiological memory in primary auditory cortex: characteristics and mechanisms

"Physiological memory" is enduring neuronal change sufficiently specific to represent learned information. It transcends both sensory traces that are detailed but transient and long-term physiological plasticities that are insufficiently specific to actually represent cardinal details of an experience. The specificity of most physiological plasticities has not been comprehensively studied. We adopted receptive field analysis from sensory physiology to seek physiological memory in the primary auditory cortex of adult guinea pigs. Receptive fields for acoustic frequency were determined before and at various retention intervals after a learning experience, typified by single-tone delay classical conditioning, e.g., 30 trials of tone-shock pairing. Subjects rapidly (5-10 trials) acquire behavioral fear conditioned responses, indexing acquisition of an association between the conditioned and the unconditioned stimuli. Such stimulus-stimulus association produces receptive field plasticity in which responses to the conditioned stimulus frequency are increased in contrast to responses to other frequencies which are decreased, resulting in a shift of tuning toward or to the frequency of the conditioned stimulus. This receptive field plasticity is associative, highly specific, acquired within a few trials, and retained indefinitely (tested to 8 weeks). It thus meets criteria for "physiological memory." The acquired importance of the conditioned stimulus is thought to be represented by the increase in tuning to this stimulus during learning, both within cells and across the primary auditory cortex. Further, receptive field plasticity develops in several tasks, one-tone and two-tone discriminative classical and instrumental conditioning (habituation produces a frequency-specific decrease in the receptive field), suggesting it as a general process for representing the acquired meaning of a signal stimulus. We have proposed a two-stage model involving convergence of the conditioned and unconditioned stimuli in the magnocellular medial geniculate of the thalamus followed by activation of the nucleus basalis, which in turn releases acetylcholine that engages muscarinic receptors in the auditory cortex. This model is supported by several recent findings. For example, tone paired with NB stimulation induces associative, specific receptive field plasticity of at least a 24-h duration. We propose that physiological memory in auditory cortex is not "procedural" memory, i.e., is not tied to any behavioral conditioned response, but can be used flexibly.     

On the role of eye movements and saccade preparation in generating auditory inhibition of return.

Examined whether the suggestion that "the eccentricity of signals which are effective in activating inhibition of return is restricted to the eccentricity to which accurate saccades can be made" is consistent with the necessary conditions for the occurrence of location-based auditory inhibition of return in a total of 24 volunteers. In 3 experiments, listeners were required to either localize or identify the 2nd of 2 successive sounds. The 1st sound and the 2nd sound could originate from either the same or different locations, and the interval between the onsets of the 2 sounds (Stimulus Onset Asynchrony, SOA) was varied. Sounds were presented out of visual range at 135 azimuth left or right. In Exp 1, localization responses were made more quickly at 100 ms SOA when the target sounded from the same location as the cue, and at 700 ms SOA when the target and cue sounded from different locations. In Exps 2 and 3, Ss monitored visual information presented directly in front of them at the same time as the auditory cue and target were presented behind them. Results indicate that in both experiments, a transition from facilitation at a brief SOA to inhibition at a longer SOA was observed for the auditory task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrophysiological evidence for the "missing link" in crossmodal attention.

Notes that orienting attention involuntarily to the location of a sensory event influences responses to subsequent stimuli that appear in different modalities with one possible exception; orienting attention involuntarily to a sudden light sometimes fails to affect responses to subsequent sounds (e.g., C. Spence and J. Driver, 1997). Here the authors investigated the effects of involuntary attention to a brief flash on the processing of subsequent sounds in a design that eliminates stimulus–response compatibility effects and criterion shifts as confounding factors. 13 18–31 yr olds participated in the study. In addition, the neural processes mediating crossmodal attention were studied by recording event-related brain potentials. The data show that orienting attention to the location of a spatially nonpredictive visual cue modulates behavioral and neural responses to subsequent auditory targets when the stimulus onset asynchrony is short (between 100 and 300 ms). These findings are consistent with the hypothesis that involuntary shifts of attention are controlled by supramodal brain mechanisms rather than by modality-specific ones. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of environmental sound familiarity on dynamic neural activation/inhibition patterns: an ERD mapping study

The aim of this study was to analyze the timing and topography of brain activity in relation to the cognitive processing of different types of auditory information. We specifically investigated the effects of familiarity on environmental sound identification, an issue which has been little studied with respect to cognitive processes, neural substrates, and time course of brain activity. To address this issue, we implemented and applied an electroencephalographic mapping method named event-related desynchronization, which allows one to assess the dynamics of neuronal activity with high temporal resolution (here, 125 ms); we used 19 recording electrodes with standard positioning. We designed an activation paradigm in which healthy subjects were asked to discriminate binaurally heard sounds belonging to one of two distinct categories, "familiar" (i.e., natural environmental sounds) or "unfamiliar" (i.e., altered environmental sounds). The sounds were selected according to strict preexperimental tests so that the former should engage greater semantic, and the latter greater structural, analysis, which we predicted to preferentially implicate left posterior and right brain regions, respectively. During the stimulations, significant desynchronizations (thought to reflect neuronal activations) were recorded over left hemisphere regions for familiar sounds and right temporofrontal regions for unfamiliar sounds, but with only few significant differences between the two sound categories and a common bilateral activation in the frontal regions. However, strongly significant differences between familiar and unfamiliar sounds occurred near the end of and following the stimulations, due to synchronizations (though to reflect deactivations) which appeared over the left posterior regions, as well as the vertex and bilateral frontal cortex, only after unfamiliar sounds. These unexpected synchronizations after the unfamiliar stimuli may reflect an awareness of the unfamiliarity of such sounds, which may have induced an inhibition of semantic and episodic representations because the latter could not be associated with meaningless sounds.     

Impaired precision, but normal retention, of auditory sensory ("echoic") memory information in schizophrenia

Working memory is the type of memory that allows one to hold information in mind while working on a task or problem. The present study investigated attention-independent auditory sensory ("echoic") memory in 18 schizophrenic participants and 17 controls. Schizophrenic participants showed impaired delayed tone matching performance in comparison with controls. However, when groups were matched for performance at 1 s by varying the difficulty of the task across groups, schizophrenic participants showed normal retention of information as reflected in normal tone matching performance. These findings demonstrate that schizophrenic may be in the sensitivity of the system rather than the duration for which memory traces were retained.     

Human salmonellosis in Singapore

1. Cats with one cochlea destroyed were trained to localize sound. After behavioral measures of the animal's accuracy of localization were made, cortical auditory areas were ablated unilaterally. 2. The results showed: a) like binaural localization, monaural localization of sound in space, as measured by the ability of an animal to move toward a sound source, depends on integrity of auditory cortex; b) it is only ablation of cortex contralateral to the functional ear that seriously affects localizing behavior; ablation of cortex ipsilateral to the intact cochlea has little or no effect on localizing behavior. 3. To explain the results, we suggest that auditory cortex is essential for an organized perception of space including the relation of the animal's position to other objects in space. We also suggest that auditory cortex contralateral to a given ear is necessary in order for the animal to recognize that a stimulus is presented to that ear of, when both ears are intact, to recognize that the stimulus to the given ear differs in some way (intensity, time of arrival, sequential arrangement of sounds) from the stimulus to the opposite ear.     

Deviant auditory stimuli activate human left and right auditory cortex differently

Infrequent "deviant' auditory stimuli embedded in a homogeneous sequence of "standard' sounds evoke a neuromagnetic mismatch field (MMF), which is assumed to reflect automatic change detection in the brain. We investigated whether MMFs would reveal hemispheric differences in cortical auditory processing. Seven healthy adults were studied with a whole-scalp neuromagnetometer. The sound sequence, delivered to one ear at time, contained three infrequent deviants (differing from standards in duration, frequency, or interstimulus interval) intermixed with standard tones. MMFs peaked 9-34 msec earlier in the right than in the left hemisphere, irrespective of the stimulated ear. Whereas deviants activated only one MMF source in the left hemisphere, two temporally overlapping but spatially separate sources, one in the temporal lobe and another in the inferior parietal cortex, were necessary to explain the right-hemisphere MMFs. We suggest that the bilateral MMF components originating in the supratemporal cortex are feature specific whereas the right-hemisphere parietal component reflects more global auditory change detection. The results imply hemispheric differences in sound processing and suggest stronger involvement of the right than the left hemisphere in change detection.     

Toward a neurophysiological theory of auditory stream segregation.

Auditory stream segregation (or streaming) is a phenomenon in which 2 or more repeating sounds differing in at least 1 acoustic attribute are perceived as 2 or more separate sound sources (i.e., streams). This article selectively reviews psychophysical and computational studies of streaming and comprehensively reviews more recent neurophysiological studies that have provided important insights into the mechanisms of streaming. On the basis of these studies, segregation of sounds is likely to occur beginning in the auditory periphery and continuing at least to primary auditory cortex for simple cues such as pure-tone frequency but at stages as high as secondary auditory cortex for more complex cues such as periodicity pitch. Attention-dependent and perception-dependent processes are likely to take place in primary or secondary auditory cortex and may also involve higher level areas outside of auditory cortex. Topographic maps of acoustic attributes, stimulus-specific suppression, and competition between representations are among the neurophysiological mechanisms that likely contribute to streaming. A framework for future research is proposed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cortical Responses in Rats Predict Perceptual Sensitivities to Complex Sounds.

The common assumption that perceptual sensitivities are related to neural representations of sensory stimuli has seldom been directly demonstrated. The authors analyzed the similarity of spike trains evoked by complex sounds in the rat auditory cortex and related cortical responses to performance in an auditory task. Rats initially learned to identify 2 highly different periodic, frequency-modulated sounds and then were tested with increasingly similar sounds. Rats correctly classified most novel sounds; their accuracy was negatively correlated with acoustic similarity. Rats discriminated novel sounds with slower modulation more accurately than sounds with faster modulation. This asymmetry was consistent with similarities in cortical representations of the sounds, demonstrating that perceptual sensitivities to complex sounds can be predicted from the cortical responses they evoke. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exploring auditory saltation using the "reduced-rabbit" paradigm.

Sensory saltation is a spatiotemporal illusion in which the judged positions of stimuli are shifted toward subsequent stimuli that follow closely in time. So far, studies on saltation in the auditory domain have usually employed subjective rating techniques, making it difficult to exactly quantify the extent of saltation. In this study, temporal and spatial properties of auditory saltation were investigated using the "reduced-rabbit" paradigm and a direct-location method. In 3 experiments, listeners judged the position of the 2nd sound within sequences of 3 short sounds by using a hand pointer. When the delay between the 2nd and 3rd sound was short, the target sound was shifted toward the subsequent sound. The magnitude of displacement increased when the temporal and spatial distance between the sounds was reduced. In a 4th experiment, a modified reduced-rabbit paradigm was used to test the hypothesis that auditory saltation is associated with an impairment of target sound localization. The findings are discussed with regard to a spatiotemporal integration approach in which the processing of auditory information is combined with information from subsequent stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Trial-to-trial carryover in auditory short-term memory.

Using a short-term recognition memory task, the authors evaluated the carryover across trials of 2 types of auditory information: the characteristics of individual study sounds (item information) and the relationships between the study sounds (study set homogeneity). On each trial, subjects heard 2 successive broadband study sounds and then decided whether a subsequently presented probe sound had been in the study set. On some trials, the similarity of the probe item to stimuli presented on the preceding trial was manipulated. This item information interfered with recognition, and false alarms increased from 0.4% to 4.4%. Moreover, the interference was tuned so that only stimuli that were very similar to each other interfered. On other trials, the relationship among stimuli was manipulated to alter the criterion subjects used in making recognition judgments. The effect of this manipulation was confined to the trial on which the criterion change was generated and did not affect the subsequent trial. These results demonstrate the existence of a sharply tuned carryover of auditory item information but no carryover of the effects of study set homogeneity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Order and disorder in auditory cortical maps

Recent physiological experiments suggest that several basic receptive field properties of neurons show non-uniform spatial distributions in the primary auditory cortex of cats and primates. The spatial distribution patterns of some of these receptive field parameters are suggestive of a parallel coding scheme for processing sound information onto several superimposed cortical 'maps'. The representations of these parameters in the auditory cortex are compatible with general features of self-organizing mapping algorithms, as the spatial representations exhibit global parameter gradients with overlaid functional patchiness. Recent studies have also revealed that within a 'representational' map, the degree of local coherence varies over a wide range and that the map can contain a substantial degree of disorder in its parametric representation of sounds. Although the causes and consequences of this representational disorder are not known, it may reflect yet unresolved organizational principles in the auditory cortex.