Periodicity coding in the primary auditory cortex of the Mongolian gerbil (Meriones unguiculatus): two different coding strategies for pitch and rhythm?

Periodic envelope or amplitude modulations (AM) with periodicities up to several thousand Hertz are characteristic for many natural sounds. Throughout the auditory pathway, signal periodicity is evident in neuronal discharges phase-locked to the envelope. In contrast to lower levels of the auditory pathway, cortical neurons do not phase-lock to periodicities above about 100 Hz. Therefore, we investigated alternative coding strategies for high envelope periodicities at the cortical level. Neuronal responses in the primary auditory cortex (AI) of gerbils to tones and AM were analysed. Two groups of stimuli were tested: (1) AM with a carrier frequency set to the unit's best frequency evoked phase-locked responses which were confined to low modulation frequencies (fms) up to about 100 Hz, and (2) AM with a spectrum completely outside the unit's frequency-response range evoked completely different responses that never showed phase-locking but a rate-tuning to high fms (50 to about 3000 Hz). In contrast to the phase-locked responses, the best fms determined from these latter responses appeared to be topographically distributed, reflecting a periodotopic organization in the AI. Implications of these results for the cortical representation of the perceptual qualities rhythm, roughness and pitch are discussed.     

Neuronal mechanisms of auditory backward recognition masking in macaque auditory cortex

The sensation of a single sound event can be altered by subsequent sounds. This study searched for neural mechanisms of such retroactive effects in macaque auditory cortex by comparing neural responses to single tones with responses to two consecutive tones. Retroactive influences were found to affect late parts of the response to a tone, which comprised 53/134 of the recordings of action potentials and 88/131 of the recordings of field potentials performed in primary, caudal, and medial auditory fields. If before or during the occurrence of the late response to the first tone a second tone was presented the late response was suppressed. Suppression of late cortical responses parallels perceptual phenomena like backward recognition masking, suggesting that suppression of late responses provides a neural correlate of auditory backward effects.     

Spectral envelope coding in cat primary auditory cortex: linear and non-linear effects of stimulus characteristics

Electrophysiological studies in mammal primary auditory cortex have demonstrated neuronal tuning and cortical spatial organization based upon spectral and temporal qualities of the stimulus including: its frequency, intensity, amplitude modulation and frequency modulation. Although communication and other behaviourally relevant sounds are usually complex, most response characterizations have used tonal stimuli. To better understand the mechanisms necessary to process complex sounds, we investigated neuronal responses to a specific class of broadband stimuli, auditory gratings or ripple stimuli, and compared the responses with single tone responses. Ripple stimuli consisted of 150-200 frequency components with the intensity of each component adjusted such that the envelope of the frequency spectrum is sinusoidal. It has been demonstrated that neurons are tuned to specific characteristics of those ripple stimulus including the intensity, the spacing of the peaks, and the location of the peaks and valleys (C. E. Schreiner and B. M. Calhoun, Auditory Neurosci., 1994; 1: 39-61). Although previous results showed that neuronal response strength varied with the intensity and the fundamental frequency of the stimulus, it is shown here that the relative response to different ripple spacings remains essentially constant with changes in the intensity and the fundamental frequency. These findings support a close relationship between pure-tone receptive fields and ripple transfer functions. However, variations of other stimulus characteristics, such as spectral modulation depth, result in non-linear alterations in the ripple transformation. The processing between the basilar membrane and the primary auditory cortex of broadband stimuli appears generally to be non-linear, although specific stimulus qualities, including the phase of the spectral envelope, are processed in a nearly linear manner.     

Involvement of cyclic GMP in the mode of action of a new antithrombotic agent PCA-4230; inhibition of the platelet cyclic GMP dependent phosphodiesterase

The division of the auditory cortex into various fields, functional aspects of these fields, and neuronal coding in the primary auditory cortical field (AI) are reviewed with stress on features that may be common to mammals. On the basis of 14 topographies and clustered distributions of neuronal response characteristics in the primary auditory cortical field, a hypothesis is developed of how a certain complex acoustic pattern may be encoded in an equivalent spatial activity pattern in AI, generated by time-coordinated firing of groups of neurons. The auditory cortex, demonstrated specifically for AI, appears to perform sound analysis by synthesis, i.e. by combining spatially distributed coincident or time-coordinated neuronal responses. The dynamics of sounds and the plasticity of cortical responses are considered as a topic for research.     

The easy-to-hard effect in human (Homo sapiens) and rat (Rattus norvegicus) auditory identification.

The authors examined whether progressively training humans and rats to perform a difficult auditory identification task led to larger improvements than extensive training with highly similar sounds (the easy-to-hard effect). Practice improved humans' ability to distinguish sounds regardless of the training regimen. However, progressively trained subjects were more accurate and showed more generalization, despite significantly less training with the stimuli that were the most difficult to distinguish. Rats showed less capacity to improve with practice but still benefited from progressive training. These findings indicate that transitioning from an easier to a more difficult task during training can facilitate, and in some cases may be essential for, auditory perceptual learning. The results are not predicted by an explanation that assumes interaction of generalized excitation and inhibition but are consistent with a hierarchical account of perceptual learning in which the representational precision required to distinguish stimuli determines the mechanisms engaged during learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Representation of spectral and temporal sound features in three cortical fields of the cat. Similarities outweigh differences

This study investigates the degree of similarity of three different auditory cortical areas with respect to the coding of periodic stimuli. Simultaneous single- and multiunit recordings in response to periodic stimuli were made from primary auditory cortex (AI), anterior auditory field (AAF), and secondary auditory cortex (AII) in the cat to addresses the following questions: is there, within each cortical area, a difference in the temporal coding of periodic click trains, amplitude-modulated (AM) noise bursts, and AM tone bursts? Is there a difference in this coding between the three cortical fields? Is the coding based on the temporal modulation transfer function (tMTF) and on the all-order interspike-interval (ISI) histogram the same? Is the perceptual distinction between rhythm and roughness for AM stimuli related to a temporal versus spatial representation of AM frequency in auditory cortex? Are interarea differences in temporal response properties related to differences in frequency tuning? The results showed that: 1) AM stimuli produce much higher best modulation frequencies (BMFs) and limiting rates than periodic click trains. 2) For periodic click trains and AM noise, the BMFs and limiting rates were not significantly different for the three areas. However, for AM tones the BMF and limiting rates were about a factor 2 lower in AAF compared with the other areas. 3) The representation of stimulus periodicity in ISIs resulted in significantly lower mean BMFs and limiting rates compared with those estimated from the tMTFs. The difference was relatively small for periodic click trains but quite large for both AM stimuli, especially in AI and AII. 4) Modulation frequencies <20 Hz were represented in the ISIs, suggesting that rhythm is coded in auditory cortex in temporal fashion. 5) In general only a modest interdependence of spectral- and temporal-response properties in AI and AII was found. The BMFs were correlated positively with characteristic frequency in AAF. The limiting rate was positively correlated with the frequency-tuning curve bandwidth in AI and AII but not in AAF. Only in AAF was a correlation between BMF and minimum latency was found. Thus whereas differences were found in the frequency-tuning curve bandwidth and minimum response latencies among the three areas, the coding of periodic stimuli in these areas was fairly similar with the exception of the very poor representation of AM tones in AII. This suggests a strong parallel processing organization in auditory cortex.     

Electrophysiologic analysis of the functional organization of cortico-cerebellar connections

The influence of associative (orbital-anterior, parietal) and projective (auditory, sensomotor) cerebral cortex areas stimulation on activity of the Purkinje neurons of cerebellar cortex was studied in adult cats under chloralose-nembutal or nembutal anesthesia. These reactions were compared with the responses to peripheral stimuli. Definite similarity in responses of the Purkinje cells to different cortical (associative, projective) stimuli was found both for types of neurons and their responsiveness. In responses of the Purkinje cells to peripheral stimulation there was no sharp similarity as it was in responses to cortical stimuli. So, in cortical stimulation almost similar number of neurons (above 50%) was excited and in peripheral stimulation the responsiveness of neurons had marked difference: to electrical stimulation of skin there were 44.6%, to auditory 34.2%, to visual 18.8% of neuron responses.     

Auditory Categorization of Complex Sounds by Rats (Rattus norvegicus).

Little research has explored the auditory categorization abilities of mammals. To better understand these processes, the authors tested the abilities of rats (Rattus norvegicus) to categorize multidimensional acoustic stimuli by using a classic category-learning task developed by R. N. Shepard, C. I. Hovland, and H. M. Jenkins (1961). Rats proved to be able to categorize 8 complex sounds on the basis of either the direction or rate of frequency modulation but not on the basis of the range of frequency modulation. Rats' categorization abilities were limited but improved slowly and incrementally, suggesting that learning was not facilitated by selective attention to acoustic dimensions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual organization of complex auditory sequences: Effect of number of simultaneous subsequences and frequency separation.

Previous findings on streaming are generalized to sequences composed of more than 2 subsequences. A new paradigm identified whether listeners perceive complex sequences as a single unit (integrative listening) or segregate them into 2 (or more) perceptual units (stream segregation). Listeners heard 2 complex sequences, each composed of 1, 2, 3, or 4 subsequences. Their task was to detect a temporal irregularity within 1 subsequence. In Experiment 1, the smallest frequency separation under which listeners were able to focus on 1 subsequence was unaffected by the number of co-occurring subsequences; nonfocused sounds were not perceptually organized into streams. In Experiment 2, detection improved progressively, not abruptly, as the frequency separation between subsequences increased from 0.25 to 6 auditory filters. The authors propose a model of perceptual organization of complex auditory sequences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Generalized auditory same-different discrimination by pigeons.

Three pigeons were trained in a successive same/different (S/D) procedure using compound auditory stimuli (pitch/timbre combinations). Using a go/no-go procedure, pigeons successfully learned to discriminate between sequences of either all same (AAAA...or BBBB...) or all different (ABCD...) sequences consisting of 12 sounds. Both pitch and timbre were subsequently established as controlling dimensions. Transfer tests with novel stimuli revealed a generalized basis for the discrimination (novel pitch/timbre combinations, novel pitches, novel instruments, and complex natural & man-made sounds). These results indicate for the first time that pigeons can learn generalized same/different discriminations in a nondominant modality. When combined with earlier visual results, they support a qualitative similarity among birds and primates in their capacity to judge this type of fundamental stimulus relation across different modalities. (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.     

Functional MRI reveals spatially specific attentional modulation in human primary visual cortex

Selective visual attention can strongly influence perceptual processing, even for apparently low-level visual stimuli. Although it is largely accepted that attention modulates neural activity in extrastriate visual cortex, the extent to which attention operates in the first cortical stage, striate visual cortex (area V1), remains controversial. Here, functional MRI was used at high field strength (3 T) to study humans during attentionally demanding visual discriminations. Similar, robust attentional modulations were observed in both striate and extrastriate cortical areas. Functional mapping of cortical retinotopy demonstrates that attentional modulations were spatially specific, enhancing responses to attended stimuli and suppressing responses when attention was directed elsewhere. The spatial pattern of modulation reveals a complex attentional window that is consistent with object-based attention but is inconsistent with a simple attentional spotlight. These data suggest that neural processing in V1 is not governed simply by sensory stimulation, but, like extrastriate regions, V1 can be strongly and specifically influenced by attention.     

Perceptual organization of acoustic stimuli by budgerigars (Melopsittacus undulatus): II. Vocal signals.

Operant conditioning and multidimensional scaling procedures were used to study auditory perception of complex sounds in the budgerigar. In a same–different discrimination task, budgerigars learned to discriminate among natural vocal signals. Multidimensional scaling procedures were used to arrange these complex acoustic stimuli in a two-dimensional space reflecting perceptual organization. Results show that budgerigars group vocal stimuli according to functional and acoustical categories. Studies with only contact calls show that birds also make within-category discriminations. The acoustic cues in contact calls most salient to budgerigars appear to be quite complex. There is a suggestion that the sex of the signaler may also be encoded in these calls. The results from budgerigars were compared with the results from humans tested on some of the same sets of complex sounds. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Psychophysics of the McGurk and other audiovisual speech integration effects.

When the auditory and visual components of spoken audiovisual nonsense syllables are mismatched, perceivers produce four different types of perceptual responses, auditory correct, visual correct, fusion (the so-called McGurk effect), and combination (i.e., two consonants are reported). Here, quantitative measures were developed to account for the distribution of the four types of perceptual responses to 384 different stimuli from four talkers. The measures included mutual information, correlations, and acoustic measures, all representing audiovisual stimulus relationships. In Experiment 1, open-set perceptual responses were obtained for acoustic /bɑ/ or /lɑ/ dubbed to video /bɑ, dɑ, gɑ, vɑ, zɑ, lɑ, wɑ, eɑ/. The talker, the video syllable, and the acoustic syllable significantly influenced the type of response. In Experiment 2, the best predictors of response category proportions were a subset of the physical stimulus measures, with the variance accounted for in the perceptual response category proportions between 17% and 52%. That audiovisual stimulus relationships can account for perceptual response distributions supports the possibility that internal representations are based on modality-specific stimulus relationships. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Embodied auditory perception: The emotional impact of approaching and receding sound sources.

Research has shown the existence of perceptual and neural bias toward sounds perceived as sources approaching versus receding a listener. It has been suggested that a greater biological salience of approaching auditory sources may account for these effects. In addition, these effects may hold only for those sources critical for our survival. In the present study, we bring support to these hypotheses by quantifying the emotional responses to different sounds with changing intensity patterns. In 2 experiments, participants were exposed to artificial and natural sounds simulating approaching or receding sources. The auditory-induced emotional effect was reflected in the performance of participants in an emotion-related behavioral task, their self-reported emotional experience, and their physiology (electrodermal activity and facial electromyography). The results of this study suggest that approaching unpleasant sound sources evoke more intense emotional responses in listeners than receding ones, whereas such an effect of perceived sound motion does not exist for pleasant or neutral sound sources. The emotional significance attributed to the sound source itself, the loudness of the sound, and loudness change duration seem to be relevant factors in this disparity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Duplex perception: A comparison of monosyllables and slamming doors.

Duplex perception has been interpreted as revealing distinct systems for general auditory perception and speech perception. The systems yield distinct experiences of the same acoustic signal, one conforming to the acoustic structure itself and the other to its source in vocal-tract activity. However, this interpretation has not been tested by examining whether duplex perception can be obtained for nonspeech sounds that are not plausibly perceived by a specialized system. In 5 experiments, some of the phenomena associated with duplex perception of speech are replicated using the sound of a slamming door. Similarities between 26 university students' responses to syllables and door sounds are striking enough to suggest that some conclusions in the speech literature should be tempered that (1) duplex perception is special to sounds for which there are perceptual modules and (2) duplex perception occurs because distinct systems have rendered different percepts of the same acoustic signal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adaptive sex differences in auditory motion perception: Looming sounds are special.

In 4 experiments, the authors examined sex differences in audiospatial perception of sounds that moved toward and away from the listener. Experiment 1 showed that both men and women underestimated the time-to-arrival of full-cue looming sounds. However, this perceptual bias was significantly stronger among women than among men. In Experiment 2, listeners estimated the terminal distance of sounds that approached but stopped before reaching them. Women perceived the looming sounds as closer than did men. However, in Experiment 3, with greater statistical power, the authors found no sex difference in the perceived distance of sounds that traveled away from the listener, demonstrating a sex-based specificity for auditory looming perception. Experiment 4 confirmed these results using equidistant looming and receding sounds. The findings suggest that sex differences in auditory looming perception are not due to general differences in audiospatial ability, but rather illustrate the environmental salience and evolutionary importance of perceiving looming objects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perception of mistuned harmonics in complex sounds by the bullfrog (Rana catesbeiana).

The ability of 73 male bullfrogs (Rana catesbeiana) to detect single mistuned harmonics in an otherwise periodic signal was studied. Bullfrogs in their natural environment were presented with playbacks of synthetic signals, resembling their species advertisement calls, that differed in the frequency of 1 harmonic component (out of 22). There were significant differences in the number and latency of the males' evoked vocal responses to these stimuli, suggesting that males were sensitive to the differences between the sounds. Differences in envelope shape (rate and depth of amplitude modulation) produced by the harmonic mistunings may underlie the differences in response. Frogs, like birds and humans, can discriminate sounds on the basis of harmonic structure, indicating that this is a general perceptual trait shared among vertebrates. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The modulation of play fighting in rats: Role of the motor cortex.

The cortex is not necessary for rats to engage in play fighting, but it is necessary for them to modify their pattern of play fighting in different contexts. Two experiments were conducted to determine the role of the motor cortex (MC). Rats with bilateral ablations of the MC performed on Postnatal Day 10 failed to show the normally present age-related modulation in defense but were able to modulate defense with different social partners. This latter finding was confirmed in rats given ablations as adults, in which responses to social status could be monitored before and after brain damage. It appears that different forms of cortical modulation of play fighting involve different cortical circuits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The language environment of the young infant: Implications for early perceptual development.

Reviews recent research on young infants' use of auditory information during early language processing. Evidence indicates that infants actively process sounds, particularly those with acoustic attributes of their native language. Infants' prenatal experience with maternal speech may determine the early postnatal perceptual salience of a specific mother's speech, motherese speech, and native speech. Infants' sensitivity to suprasegmental aspects of speech may dictate much of what they attend to, while features of infant-directed speech seem to draw their attention to the speaker and elicit positive affective responses. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)