Biomedical subjects

G H Recanzone

Publications and source records attributed to G H Recanzone.

At least 19 recordsLinked to original sources

PubMed2001

Temporal and spatial dependency of the ventriloquism effect.

The perception of the spatial location of an auditory stimulus can be captured by a spatially disparate visual stimulus, a phenomenon known as the ventriloquism effect. This study investigated the temporal and spatial dependency of this illusion. In the temporal domain, only disparities of 50-100 ms were perceived as simultaneous, and disparities where the visual stimulus occurred before the auditory stimulus were more effective in creating the illusion. In the spatial domain, the illusion was elicited most strongly at spatial disparities below spatial discrimination thresholds. There was also a significant interaction between temporal and spatial disparities. These results indicate that both temporal and spatial parameters are critical in the perception of real world objects in extrapersonal space.

Acoustic Stimulation↗

PubMed2001

Differential effect of near-threshold stimulus intensities on sound localization performance in azimuth and elevation in normal human subjects.

The ability of humans to localize sounds remains relatively constant across a range of intensities well above detection threshold, and increasing the spectral content of the stimulus results in an improvement in localization ability. For broadband stimuli, intensities near detection threshold result in fewer and weaker binaural cues used in azimuth localization because the stimulus energy at the high- and low-frequency ends of the audible spectrum fall below detection threshold. Thus, the ability to localize broadband sounds in azimuth is predicted to be degraded at audible but near threshold stimulus intensities. The spectral cues for elevation localization (spectral peaks and notches generated by the head-related transfer function) span a narrower frequency range than those for azimuth. As the stimulus intensity decreases, the ability to detect the stimulus frequencies corresponding to the spectral notches will be more strongly affected than the ability to detect frequencies outside the range where these spectral cues are useful. Consequently, decreasing the stimulus intensity should degrade localization in both azimuth and elevation and create a greater deficit in elevation localization due to the narrower band of audible frequencies containing elevation cues compared to azimuth cues. The present study measured the ability of 11 normal human subjects to localize broadband noise stimuli along the midsagittal plane and horizontal meridian at stimulus intensities of 14, 22, and 30 dB above the subject's detection threshold using a go/no-go behavioral paradigm. Localization ability decreased in both azimuth and elevation with decreasing stimulus intensity, and this effect was greater on localization in elevation than on localization in azimuth. The differential effects of stimulus intensity on sound localization in azimuth and elevation found in the present study may provide a valuable tool in investigating the neural correlates of sound location perception.

Adult↗

PubMed2001

Hearing and looking.

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Acoustic Stimulation↗

PubMed2000

Spatial processing in the auditory cortex of the macaque monkey.

The patterns of cortico-cortical and cortico-thalamic connections of auditory cortical areas in the rhesus monkey have led to the hypothesis that acoustic information is processed in series and in parallel in the primate auditory cortex. Recent physiological experiments in the behaving monkey indicate that the response properties of neurons in different cortical areas are both functionally distinct from each other, which is indicative of parallel processing, and functionally similar to each other, which is indicative of serial processing. Thus, auditory cortical processing may be similar to the serial and parallel "what" and "where" processing by the primate visual cortex. If "where" information is serially processed in the primate auditory cortex, neurons in cortical areas along this pathway should have progressively better spatial tuning properties. This prediction is supported by recent experiments that have shown that neurons in the caudomedial field have better spatial tuning properties than neurons in the primary auditory cortex. Neurons in the caudomedial field are also better than primary auditory cortex neurons at predicting the sound localization ability across different stimulus frequencies and bandwidths in both azimuth and elevation. These data support the hypothesis that the primate auditory cortex processes acoustic information in a serial and parallel manner and suggest that this may be a general cortical mechanism for sensory perception.

Acoustic Stimulation↗

PubMed2000

Response profiles of auditory cortical neurons to tones and noise in behaving macaque monkeys.

The primate auditory cortex is anatomically divided into several areas, but little is known about the functional differences between these areas. Similarly, although neurons in sub-cortical auditory areas of other species have been classified into distinct categories, these criteria have not been applied in primates. This study measured the responses of single neurons in the primary auditory cortex (AI) and the caudomedial field (CM) to tones and noise. Most neurons could be qualitatively classified as onset, sustained, or sustained-onset, but never as primary (VIII nerve)-like or chopper. Quantitative analysis showed a continuum of response types, from having only onset responses to responding throughout the stimulus period. AI neurons had higher firing rates that CM neurons, but CM neurons had higher firing rates to noise stimuli compared to tone stimuli, and a greater percentage of CM neurons had excitatory responses after stimulus offset. There were no differences in the percentage of neurons that had tonic or inhibitory responses. These results indicate that the responses of neurons in the primate auditory cortex are better described as a continuum rather than as discrete classes, and provide further evidence that auditory information is processed in series between AI and CM in the primate.

Acoustic Stimulation↗

PubMed2000

Effects of attention on MT and MST neuronal activity during pursuit initiation.

The responses of neurons in monkey extrastriate areas MT (middle temporal) and MST (medial superior temporal), and the initial metrics of saccadic and pursuit eye movements, have previously been shown to be better predicted by vector averaging or winner-take-all models depending on the stimulus conditions. To investigate the potential influences of attention on the neuronal activity, we measured the responses of single MT and MST neurons under identical stimulus conditions when one of two moving stimuli was the target for a pursuit eye movement. We found the greatest attentional modulation across neurons when two stimuli moved through the receptive field (RF) of the neuron and the stimulus motion was initiated at least 450 ms before reaching the center of the RF. These conditions were the same as those in which a winner-take-all model better predicted both the eye movements and the underlying neuronal activity. The modulation was almost always an increase of activity, and it was about equally frequent in MT and MST. A modulation of >50% was observed in approximately 41% of MT neurons and 27% of MST neurons. Responses to all directions of motion were modulated so that the direction tuning curves in the attended and unattended conditions were similar. Changes in the background activity with target selection were small and unlikely to account for the observed attentional modulation. In contrast, there was little change in the neuronal response with attention when the stimulus reached the RF center 150 ms after motion onset, which was also the condition in which the vector average model better predicted the initial eye movements and the activity of the neurons. These results are consistent with a competition model of attention in which top-down attention acts on the activity of one of two competing populations of neurons activated by the bottom-up input from peripheral stimuli. They suggest that there is a minimal separation of the populations necessary before attention can act on one population, similar to that required to produce a winner-take-all mode of behavior in pursuit initiation. The present experiments also suggest that it takes several hundred milliseconds to develop this top-down attention effect.

Animals↗

PubMed2000

Frequency and intensity response properties of single neurons in the auditory cortex of the behaving macaque monkey.

Response properties of auditory cortical neurons measured in anesthetized preparations have provided important information on the physiological differences between neurons in different auditory cortical areas. Studies in the awake animal, however, have been much less common, and the physiological differences noted may reflect differences in the influence of anesthetics on neurons in different cortical areas. Because the behaving monkey is gaining popularity as an animal model in studies exploring auditory cortical function, it has become critical to physiologically define the response properties of auditory cortical neurons in this preparation. This study documents the response properties of single cortical neurons in the primary and surrounding auditory cortical fields in monkeys performing an auditory discrimination task. We found that neurons with the shortest latencies were located in the primary auditory cortex (AI). Neurons in the rostral field had the longest latencies and the narrowest intensity and frequency tuning, neurons in the caudomedial field had the broadest frequency tuning, and neurons in the lateral field had the most monotonic rate/level functions of the four cortical areas studied. These trends were revealed by comparing response properties across the population of studied neurons, but there was considerable variability between neurons for each response parameter other than characteristic frequency (CF) in each cortical area. Although the neuronal CFs showed a systematic spatial organization across AI, no such systematic organization was apparent for any other response property in AI or the adjacent cortical areas. The results of this study indicate that there are physiological differences between auditory cortical fields in the behaving monkey consistent with previous studies in the anesthetized animal and provide insights into the functional role of these cortical areas in processing acoustic information.

Action Potentials↗

PubMed2000

Correlation between the activity of single auditory cortical neurons and sound-localization behavior in the macaque monkey.

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, we studied the responses of single neurons in the primary auditory cortex (AI) and the caudomedial field (CM) of two monkeys while they performed a sound-localization task. Regression analysis indicated that the responses of approximately 80% of neurons in both cortical areas were significantly correlated with the azimuth or elevation of the stimulus, or both, which we term "spatially sensitive." The proportion of spatially sensitive neurons was greater for stimulus azimuth compared with stimulus elevation, and elevation sensitivity was primarily restricted to neurons that were tested using stimuli that the monkeys also could localize in elevation. Most neurons responded best to contralateral speaker locations, but we also encountered neurons that responded best to ipsilateral locations and neurons that had their greatest responses restricted to a circumscribed region within the central 60 degrees of frontal space. Comparing the spatially sensitive neurons with those that were not spatially sensitive indicated that these two populations could not be distinguished based on either the firing rate, the rate/level functions, or on their topographic location within AI. Direct comparisons between the responses of individual neurons and the behaviorally measured sound-localization ability indicated that proportionally more neurons in CM had spatial sensitivity that was consistent with the behavioral performance compared with AI neurons. Pooling the responses across neurons strengthened the relationship between the neuronal and psychophysical data and indicated that the responses pooled across relatively few CM neurons contain enough information to account for sound-localization ability. These data support the hypothesis that auditory space is processed in a serial manner from AI to CM in the primate cerebral cortex.

Action Potentials↗

PubMed2000

Auditory and visual spatial localization deficits following bilateral parietal lobe lesions in a patient with Balint's syndrome.

Lesion and electrophysiological studies indicate that the parietal lobes play a role in visual spatial attention and in computing the spatial coordinates of visual input. Fewer studies have investigated the role of the parietal lobe in auditory spatial processing, and an extensive comparison of visual and auditory spatial processing in humans with parietal lobe lesions has yet to be conducted. We have studied such localization abilities in a Balint's syndrome patient (RM) who has bilateral parietal lobe lesions. The results indicated that this patient had a significant deficit in both visual and auditory localization relative to age-matched controls. Unlike the controls, however, RM's auditory localization ability either matched or exceeded his visual localization ability depending on the task. Accordingly, RM exhibited "auditory capture," but not "visual capture" under conditions where control subjects showed the opposite pattern. These results are consistent with hypotheses that the parietal lobes are involved in creating multiple spatial representations and in shifting from one spatial reference point to another, but suggest that these parietal structures are not necessary for the integration of multiple sensory stimuli resulting in capture effects.

Acoustic Stimulation↗

PubMed1999

Functional organization of spectral receptive fields in the primary auditory cortex of the owl monkey.

Recent experiments in the cat have demonstrated that several response parameters, including frequency tuning, intensity tuning, and FM selectivity, are spatially segregated across the isofrequency axis. To investigate whether a similar functional organization exists in the primate, we have studied the spatial distribution of pure-tone receptive field parameters across the primary auditory cortex (AI) in six owl monkeys (Aotus trivirgatus). The distributions of binaural interaction types and onset latency were also examined. Consistent with previous studies, the primary auditory cortex contained a clear cochleotopic organization. We demonstrate here that several other properties of the responses to tonal stimuli also showed nonrandom spatial distributions that were largely independent from each other. In particular, the sharpness of frequency tuning to pure tones, intensity tuning and sensitivity, response latency, and binaural interaction types all showed spatial variations that were independent from the representation of characteristic frequency and from each other. Statistical analysis confirmed that these organizations did not reflect random distributions. The overall organizational pattern of overlaying but independent functional maps that emerged was quite similar to that seen in AI of cats and, in general, appears to reflect a fundamental organization principle of primary sensory cortical fields.

Action Potentials↗

PubMed1999

Shift in smooth pursuit initiation and MT and MST neuronal activity under different stimulus conditions.

The activity of neurons in extrastriate middle temporal (MT) and medial superior temporal (MST) areas were studied during the initiation of pursuit eye movements in macaque monkeys. The intersecting motion of two stimuli was used to test hypotheses about how these direction- and speed-sensitive neurons contribute to the generation of pursuit. The amplitude and direction of the initial saccade to the target and the initial speed and direction of pursuit were best predicted by a vector-average model of the underlying neuronal activity with relatively short time and spatial separation before a visual pursuit target and a distracter stimulus crossed in the visual field. The resulting eye movements were best described by a winner-take-all model when the time and spatial separation between the two stimuli was increased before the stimuli crossed. Neurons in MT and MST also shifted their activity from that best described by a vector average to a winner-take-all model under the same stimulus conditions. The changes in activity of neurons in both areas were generally similar to each other during these changes in pursuit initiation. Thus a slight alteration in the target motion produced a concurrent shift in both the neuronal processing and the movement execution. We propose that the differences in the oculomotor behavior can be accounted for by shifts in the overlap of active neuronal populations within MT and MST.

Analysis of Variance↗

PubMed1998

Rapidly induced auditory plasticity: the ventriloquism aftereffect.

Cortical representational plasticity has been well documented after peripheral and central injuries or improvements in perceptual and motor abilities. This has led to inferences that the changes in cortical representations parallel and account for the improvement in performance during the period of skill acquisition. There have also been several examples of rapidly induced changes in cortical neuronal response properties, for example, by intracortical microstimulation or by classical conditioning paradigms. This report describes similar rapidly induced changes in a cortically mediated perception in human subjects, the ventriloquism aftereffect, which presumably reflects a corresponding change in the cortical representation of acoustic space. The ventriloquism aftereffect describes an enduring shift in the perception of the spatial location of acoustic stimuli after a period of exposure of spatially disparate and simultaneously presented acoustic and visual stimuli. Exposure of a mismatch of 8 degrees for 20-30 min is sufficient to shift the perception of acoustic space by approximately the same amount across subjects and acoustic frequencies. Given that the cerebral cortex is necessary for the perception of acoustic space, it is likely that the ventriloquism aftereffect reflects a change in the cortical representation of acoustic space. Comparisons between the responses of single cortical neurons in the behaving macaque monkey and the stimulus parameters that give rise to the ventriloquism aftereffect suggest that the changes in the cortical representation of acoustic space may begin as early as the primary auditory cortex.

Adult↗

PubMed1998

Comparison of relative and absolute sound localization ability in humans.

Sound localization ability has traditionally been studied using either a relative localization task, where thresholds to determine a difference in sound source location is approximately 1-10 degrees, or an absolute localization task, where the range of estimates of the source of a sound are 4-30 degrees. In order to directly relate these two psychophysical methods, we compared the psychometric functions from a relative localization task in a human subject to the same subject's performance on an absolute localization task using three different acoustic stimuli: Gaussian noise, 1-kHz tones, and 4-kHz tones. The results showed that the relative localization threshold was a poor indicator of the range of estimates of the same stimulus in absolute space, however, the width of the relative localization psychometric functions was well correlated with the width of the distribution of estimates made in the absolute localization task. It is concluded that the relative localization psychometric functions, but not threshold, provides a reliable estimate of absolute spatial localization ability in human subjects, and suggested that the same neuronal mechanisms can underlie the psychophysical data using both methods.

Adult↗

PubMed1997

Responses of MT and MST neurons to one and two moving objects in the receptive field.

To test the effects of complex visual motion stimuli on the responses of single neurons in the middle temporal visual area (MT) and the medial superior temporal area (MST) of the macaque monkey, we compared the response elicited by one object in motion through the receptive field with the response of two simultaneously presented objects moving in different directions through the receptive field. There was an increased response to a stimulus moving in a direction other than the best direction when it was paired with a stimulus moving in the best direction. This increase was significant for all directions of motion of the non-best stimulus and the magnitude of the difference increased as the difference in the directions of the two stimuli increased. Similarly, there was a decreased response to a stimulus moving in a non-null direction when it was paired with a stimulus moving in the null direction. This decreased response in MT did not reach significance unless the second stimulus added to the null direction moved in the best direction, whereas in MST the decrease was significant when the second stimulus direction differed from the null by 90 degrees or more. Further analysis showed that the two-object responses were better predicted by taking the averaged response of the neuron to the two single-object stimuli than by summation, multiplication, or vector addition of the responses to each of the two single-object stimuli. Neurons in MST showed larger modulations than did neurons in MT with stimuli moving in both the best direction and in the null direction and the average better predicted the two-object response in area MST than in area MT. This indicates that areas MT and MST probably use a similar integrative mechanisms to create their responses to complex moving visual stimuli, but that this mechanism is further refined in MST. These experiments show that neurons in both MT and MST integrate the motion of all directions in their responses to complex moving stimuli. These results with the motion of objects were in sound agreement with those previously reported with the use of random dot patterns for the study of transparent motion in MT and suggest that these neurons use similar computational mechanisms in the processing of object and global motion stimuli.

Algorithms↗

PubMed1993

Alterations in correlated activity parallel ICMS-induced representational plasticity.

We studied neural interactions by cross correlation analysis during representational plasticity induced by intracortical microstimulation (ICMS). Neuron pairs were simultaneously recorded in area 3b in adult New World monkeys, and in cortical field SI in adult rats. In normal animals, the degree of correlated spontaneous activity corresponded to the extent of receptive field overlap. After several hours of ICMS, the spatial extents of cortex over which correlated activity could be recorded was enlarged several-fold. Mapping experiments revealed that increased correlated activity was only recorded within that cortical sector that was representationally reorganized, indicating a close relationship between cortical reorganization and cooperative processes. Results support the hypothesis that discharge coincidence is crucial for the formation of functionally coupled neural groups, and implicate dynamically maintained groups in the genesis of postontogenetic plasticity.

Action Potentials↗

PubMed1993

Plasticity in the frequency representation of primary auditory cortex following discrimination training in adult owl monkeys.

Previous studies have shown that the tonotopic organization of primary auditory cortex is altered subsequent to restricted cochlear lesions (Robertson and Irvine, 1989) and that the topographic reorganization of the primary somatosensory cortex is correlated with changes in the perceptual acuity of the animal (Recanzone et al., 1992a-d). Here we report an increase in the cortical area of representation of a restricted frequency range in primary auditory cortex of adult owl monkeys that is correlated with the animal's performance at a frequency discrimination task. Monkeys trained for several weeks to discriminate small differences in the frequency of sequentially presented tonal stimuli revealed a progressive improvement in performance with training. At the end of the training period, the tonotopic organization of Al was defined by recording multiple-unit responses at 70-258 cortical locations. These responses were compared to those derived from three normal monkeys and from two monkeys that received the same auditory stimuli but that were engaged in a tactile discrimination task. The cortical representation, the sharpness of tuning, and the latency of the response were greater for the behaviorally relevant frequencies of trained monkeys when compared to the same frequencies of control monkeys. The cortical area of representation was the only studied parameter that was correlated with behavioral performance. These results demonstrate that attended natural stimulation can modify the tonotopic organization of Al in the adult primate, and that this alteration is correlated with changes in perceptual acuity.

Acoustic Stimulation↗

PubMed1992

Progressive improvement in discriminative abilities in adult owl monkeys performing a tactile frequency discrimination task.

1. Adult owl monkeys were trained to detect a difference in the frequency of sequentially applied tactile stimuli presented to a constant, restricted location on the glabrous skin of a single finger. Psychophysical performance functions and thresholds were determined on daily sessions over a 3- to 20-wk-long training period. 2. Thresholds for the trained digit progressively decreased from a 6- to 8-Hz difference to a 2- to 3-Hz difference relative to a 20-Hz standard. These thresholds were similar to those described for macaques and humans determined by the use of a two-alternative forced-choice procedure. 3. Six of the seven studied monkeys showed a continuously progressive improvement in performance with training. Early in the training period, the performance improved at about the same rate for all frequencies. Later in the training period, the performance for frequencies much greater than the comparison frequency improved sooner than did the performances for frequencies more similar to the comparison frequency. This resulted in an increase of the slope of the psychometric function near threshold. In a single monkey, no clear later-component improvements were recorded. 4. Analyses of performances using the theory of signal detection revealed a progressive increase in the measure of d' for all frequencies above threshold. 5. Some improvements in performance were also recorded when stimuli were applied on an adjacent digit, which was trained for 2 or 3 sessions spaced throughout the course of training. However, thresholds on these digits were always greater than those on the trained digit. These findings suggest that there are local changes generated by this training at somatotopically restricted regions of the central somatosensory nervous system. 6. It is concluded that this training resulted in a genuine progressive improvement in temporal acuity specific to the trained skin. The initial rapid improvement was likely due to an improvement in the "strategy" or "cognitive" aspects of the task, whereas more gradual improvements in performance recorded throughout the training period were most probably due to somatotopically localized changes in the neural representations of the behaviorally relevant stimulus.

Animals↗

PubMed1992

Topographic reorganization of the hand representation in cortical area 3b owl monkeys trained in a frequency-discrimination task.

1. Adult owl monkeys were trained to detect differences in the frequency of a tactile flutter-vibration stimulus above a 20-Hz standard. All stimuli were delivered to a constant skin site restricted to a small part of a segment of one finger. The frequency-difference discrimination performance of all but one of these monkeys improved progressively with training. 2. The distributed responses of cortical neurons ("maps") of the hand surfaces were defined in detail in somatosensory cortical area 3b. Representations of trained hands were compared with those of the opposite, untrained hand, and to the area 3b representations of hands in a second set of monkeys that were stimulated tactually in the same manner while these monkeys were attending to auditory stimuli (passive stimulation controls). 3. The cortical representations of the trained hands were substantially more complex in topographic detail than the representations of unstimulated hands or of passively stimulated control hands. 4. In all well-trained monkeys the representations of the restricted skin location trained in the behavioral task were significantly (1.5 to greater than 3 times) greater in area than were the representations of equivalent skin locations on control digits. However, the overall extents of the representations of behaviorally stimulated fingers were not larger than those of control fingers in the same hemisphere, or in opposite hemisphere controls. 5. The receptive fields representing the trained skin were significantly larger than receptive fields representing control digits in all but one trained monkey. The largest receptive fields were centered in the zone of representation of the behaviorally engaged skin, but they were not limited to it. Large receptive fields were recorded in a 1- to 2-mm-wide zone in the area 3b maps of trained hands. 6. Receptive-field sizes were also statistically significantly larger on at least one adjacent, untrained digit when compared with the receptive fields recorded on the homologous digit of the opposite hand. 7. There was an increase in the percent overlaps of receptive fields in the cortical zone of representation of the trained skin. A significant number of receptive fields were centered on the behaviorally trained skin site. 8. The effects of increased topographic complexity, increased representation of the trained skin location, increased receptive-field size, and increased receptive-field overlap were not observed in the representations of the untrained hands in these same monkeys. Only modest increases in topographic complexity were recorded in the representations of passively stimulated hands, and no effects on receptive-field size or overlap were noted.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗