Depth electrode recordings show double dissociation between pitch processing in lateral Heschl’s gyrus and sound onset processing in medial Heschl’s gyrus

Pitch is a fundamental perceptual attribute of sounds. Our ability to discriminate, separate, and identify sounds relies heavily on pitch. Recent neuroimaging studies in humans have provided converging evidence for the existence of a “pitch center”—a region on the superior temporal plane (STP) lateral to Heschl’s gyrus specialized in pitch extraction—but a direct confirmation is still missing. Intracerebral recordings in humans are ideally suited for such a confirmation. Here we report results from depth electrode recordings in a patient undergoing investigation for epilepsy. We demonstrate a double dissociation between responses from the medial and lateral STP around Heschl’s gyrus to the onset of sound energy and the onset of pitch. Three pieces of evidence support this finding: (1) the response to sounds that do not contain pitch is small in the lateral STP compared to the medial STP; (2) sounds that contain pitch evoke a strong response in the lateral STP; (3) at the transition from noise to a specialised noise-like, but tonal, sound referred to as iterated ripple noise, where the onset of pitch is the sole acoustic event, only the lateral contact showed a response. Our results provide direct evidence for a pitch-specific area on lateral STP with intracranial recordings from the human auditory cortex.     

Functional properties of neurons in the temporo-parietal association cortex of awake monkey

Summary The temporo-parietal association cortex around the caudal end of the Sylvian fissure was studied with the single cell recording technique in three awake behaving Macaca speciosa-monkeys. Of the 197 cells isolated, 5% were active only during the monkey's own movements, mostly during head rotation, and 95% were responsive to sensory stimulation: 54% to auditory stimuli, 24% to somatosensory stimuli, 13% to both of these and 4% to visual stimuli. Some cells, classified as responsive to somatosensory stimuli, were activated only by passive rotation of the head on the cervical axis; it is possible that they were driven by vestibular stimuli. Half of the cells were activated by stimuli on both sides of the monkey, and almost all the rest, only by stimuli on the side contralateral to the hemisphere recorded.Of the acoustically drivable cells, 95% responded to natural sounds, such as, rubbing hands together, rustle of clothes, clicks or jingles (sounds with noise spectrum and rapid intensity transitions). Most of these neurons were also examined with pure tones of 0.2–20 kHz: various inhibitory or excitatory responses were elicited in half of them, usually over a wide range of frequencies. The responses of most acoustically drivable cells (62%) depended on the location of the sound source with reference to the monkey's head so that the maximal response was elicited by sounds with a certain angle of incidence, usually on the contralateral side.The present results suggest that the area studied participates in the analysis of the temporal pattern of a sound, the location of the sound source and in spatial control of head movements.     

Sound localization in newborn human infants

Newborns' localization of sounds was examined in two experiments that utilized different psychophysical procedures and imposed different task demands. The results of both experiments were consistent in indicating that neonates not only differentiate the hemifield of a sound source but have some capacity to localize a sound within the hemifields. Adjustment of their initial head turn angle following a within-hemifield shift in location of an ongoing sound indicated that head orientation in neonates is elicited not only by sound onset but also by changes in location of an ongoing sound. Thus, multiple stimulus parameters impact on this neonatal response. Results are related to research on sound localization in older infants, and discussed in light of early development of the central auditory system.©1994 John Wiley & Sons, Inc.     

Posture of the arm when grasping spheres to place them elsewhere

Despite the infinitely many ways to grasp a spherical object, regularities have been observed in the posture of the arm and the grasp orientation. In the present study, we set out to determine the factors that predict the grasp orientation and the final joint angles of reach-to-grasp movements. Subjects made reach-to-grasp movements toward a sphere to pick it up and place it at an indicated location. We varied the position of the sphere and the starting and placing positions. Multiple regression analysis showed that the sphere’s azimuth from the subject was the best predictor of grasp orientation, although there were also smaller but reliable contributions of distance, starting position, and perhaps even placing position. The sphere’s initial distance from the subject was the best predictor of the final elbow angle and shoulder elevation. A combination of the sphere’s azimuth and distance from the subject was required to predict shoulder angle, trunk-head rotation, and lateral head position. The starting position best predicted the final wrist angle and sagittal head position. We conclude that the final posture of the arm when grasping a sphere to place it elsewhere is determined to a larger extend by the initial position of the object than by effects of starting and placing position.     

Ultrafast tracking of sound location changes as revealed by human auditory evoked potentials

The rapid discrimination of auditory location information enables grouping and selectively attending to specific sound sources. The typical indicator of auditory change detection is the mismatch negativity (MMN) occurring at a latency of about 100-250 ms. However, recent studies have revealed the existence of earlier markers of frequency deviance detection in the middle-latency response (MLR). Here, we measured the MLR and MMN to changes in sound location. Clicks were presented in either the left or right hemifields during oddball (rare 30°-shifts in location), reversed oddball, and control (sounds occurring equiprobably from five locations) conditions. Clicks at deviant locations elicited an MMN and an enhanced Na component of the MLR peaking at 20 ms compared to clicks at standard or control locations. Whereas MMN was not significantly lateralized, the Na effect showed a contralateral dominance. These findings indicate that, also for sound location changes, early detection processes exist upstream of MMN.     

Cortical activation by monaural speech sound stimulation demonstrated by positron emission tomography

To investigate how auditory input from each ear contributes to spoken language processing, cortical activation by monaural speech sound stimulation was examined in 12 normal subjects using¹⁵O-labeled water positron emission tomography. Regional cerebral blood flow (rCBF) was measured under four different sound stimulation conditions: (1) silence, (2) white noise, (3) sequential Japanese sentences (“speech”), and (4) Japanese sentences played backward (“reversed speech”), and the results were evaluated by statistical parametric mapping (SPM). Noise induced significant rCBF increase in the contralateral Heschl’s gyrus. Speech and reversed speech stimuli caused significant rCBF increase in the contralateral Heschl’s gyrus and the bilateral superior temporal gyri, with contralateral activation broader than that in the ipsilateral hemisphere. Monaurally input speech sound signals that reach the contralateral Heschl’s gyrus may be processed chiefly and phonologically in the surrounding superior temporal gyrus in the same hemisphere. Comparison of speech activation with reversed speech activation failed to demonstrate a significant difference, which made it difficult to identify the area for lexical and semantic processing.     

Distortions of perceived auditory and visual space following adaptation to motion

Adaptation to visual motion can induce marked distortions of the perceived spatial location of subsequently viewed stationary objects. These positional shifts are direction specific and exhibit tuning for the speed of the adapting stimulus. In this study, we sought to establish whether comparable motion-induced distortions of space can be induced in the auditory domain. Using individually measured head related transfer functions (HRTFs) we created auditory stimuli that moved either leftward or rightward in the horizontal plane. Participants adapted to unidirectional auditory motion presented at a range of speeds and then judged the spatial location of a brief stationary test stimulus. All participants displayed direction-dependent and speed-tuned shifts in perceived auditory position relative to a ‘no adaptation’ baseline measure. To permit direct comparison between effects in different sensory domains, measurements of visual motion-induced distortions of perceived position were also made using stimuli equated in positional sensitivity for each participant. Both the overall magnitude of the observed positional shifts, and the nature of their tuning with respect to adaptor speed were similar in each case. A third experiment was carried out where participants adapted to visual motion prior to making auditory position judgements. Similar to the previous experiments, shifts in the direction opposite to that of the adapting motion were observed. These results add to a growing body of evidence suggesting that the neural mechanisms that encode visual and auditory motion are more similar than previously thought.     

Effects of perceptual context on event-related brain potentials during auditory spatial attention

The effects of auditory spatial attention on event-related brain potentials (ERPs) were examined in situations that promoted stream segregation. Short and long noise bursts were presented at three azimuth locations and listeners were asked to respond to the longer sounds occurring at either the right- or left-most location. In the baseline condition, the three sound sources were evenly spaced apart. In the distractor clustering conditions, middle and far sounds were clustered. In the attended clustering conditions, middle and attended sounds were clustered. ERP indices of attention, isolated as negative difference (Nd) waves, were greater over the hemisphere contralateral to the attended location. Nd waves were also larger when the middle sounds were moved toward the far distractors, consistent with an object-based gradient of auditory attention in which higher order information provided by the perceptual context influences selective processing.     

Attentional modulation of human auditory cortex

Attention powerfully influences auditory perception, but little is understood about the mechanisms whereby attention sharpens responses to unattended sounds. We used high-resolution surface mapping techniques (using functional magnetic resonance imaging, fMRI) to examine activity in human auditory cortex during an intermodal selective attention task. Stimulus-dependent activations (SDAs), evoked by unattended sounds during demanding visual tasks, were maximal over mesial auditory cortex. They were tuned to sound frequency and location, and showed rapid adaptation to repeated sounds. Attention-related modulations (ARMs) were isolated as response enhancements that occurred when subjects performed pitch-discrimination tasks. In contrast to SDAs, ARMs were localized to lateral auditory cortex, showed broad frequency and location tuning, and increased in amplitude with sound repetition. The results suggest a functional dichotomy of auditory cortical fields: stimulus-determined mesial fields that faithfully transmit acoustic information, and attentionally labile lateral fields that analyze acoustic features of behaviorally relevant sounds.     

Human sound localization: measurements in untrained,head-unrestrained subjects using gaze as a pointer

Studies of sound localization in humans have used various behavioral measures to quantify the observers’ perceptions; a non-comprehensive list includes verbal reports, head pointing, gun pointing, stylus pointing, and laser aiming. Comparison of localization performance reveals that in humans, just as in animals, different results are obtained with different experimental tasks. Accordingly, to circumvent problems associated with task selection and training, this study used gaze, an ethologically valid behavior for spatial pointing in species with a specialized area of the fovea, to measure sound localization perception of human subjects. Orienting using gaze as a pointer does not require training, preserves the natural link between perception and action, and allows for direct behavioral comparisons across species. The results revealed, unexpectedly, a large degree of variability across subjects in both accuracy and precision. The magnitude of the average angular localization errors for the most eccentric horizontal targets, however, were very similar to those documented in studies that used head pointing, whereas the magnitude of the localization errors for the frontal targets were considerably larger. In addition, an overall improvement in sound localization in the context of the memory-saccade task, as well as a lack of effect of initial eye and head position on perceived sound location were documented.     

Interhemisphere Asymmetry of Auditory Evoked Potentials in Humans and Mismatch Negativity during Sound Source Localization

Results of studies in humans of long-latency auditory evoked potentials and mismatch negativity in conditions of dichotic stimulation during presentation of deviant stimuli producing instantaneous changes in stimulus azimuth from the null to +22.5° or movement at rates of 11.25–112.5°/sec from the midline of the head across the left and right hemispheres towards each ear are presented. These studies showed that the total amplitude of the components of the N1–P2 complex of auditory evoked potentials in the frontal lead of the right hemisphere was greater than that in the left hemisphere. Mismatch negativity parameters showed significant relationships with the spatial position of the sound source, namely, its displacement into the right hemisphere from the position of the sound image of the standard signal. Questions of the involvement of the right hemisphere in discriminating the spatial characteristics of sound sources are discussed.     

Sound localisation during illusory self-rotation

Auditory elevation localisation was investigated under conditions of illusory self-rotation (i.e., vection) induced by movement of wide-field visual stimuli around participants’ z-axes. Contrary to previous findings which suggest that auditory cues to sound-source elevation are discounted during vection, we found little evidence that vection affects judgements of source elevation. Our results indicate that the percept of auditory space during vection is generally consistent with the available head-centered auditory cues to source elevation. Auditory information about the head-centered location of a source appears to be integrated, without modification, with visual information about head motion to determine the perceived exocentric location of the source.     

Influence of measurement noise and electrode mislocalisation on EEG dipole-source localisation

Measurement noise in the electro-encephalogram (EEG) and inaccurate formation about the locations of the EEG electrodes on the head induce localisation errors in the results of EEG dipole source analysis. These errors are studied by performing dipole source localisation for simulated electrode potentials in a spherical head model, for a range of different dipole locations and for two different numbers (27 and 148) of electrodes. Dipole source localisation is performed by iteratively minimising the residual energy (RE), using the simplex algorithm. The ratio of the dipole localisation error (cm) to the noise level (%) of Gaussian measurement noise amounts to 0.15 cm/% and 0.047 cm/% for the 27 and 148 electrode configurations, respectively, for a radial dipole with 40% eccentricity The localisation error due to noise can be reduced by taking into account multiple time instants of the measured potentials. In the case of random displacements of the EEG electrodes, the ratio of dipole localisation errors to electrode location errors amounts to 0.78 cm⁻¹ cm and 0.27 cm⁻¹ cm for the 27 and 148 electrode configurations, respectively. It is concluded that it is important to reduce the measurement noise, and particularly the electrode mislocalisation, as the influence of the latter is not reduced by taking into account multiple time instants.     

Differential influence of vision and proprioception on control of movement distance

The purpose of this study was to investigate the contribution of proprioceptive and visual information about initial limb position in controlling the distance of rapid, single-joint reaching movements. Using a virtual reality environment, we systematically changed the relationship between actual and visually displayed hand position as subjects’ positioned a cursor within a start circle. No visual feedback was given during the movement. Subjects reached two visual targets (115 and 125° elbow angle) from four start locations (90, 95, 100, and 105° elbow angle) under four mismatch conditions (0, 5, 10, or 15°). A 2×4×4 ANOVA enabled us to ask whether the subjects controlled the movement distance in accord with the virtual, or the actual hand location. Our results indicate that the movement distance was mainly controlled according to the virtual start location. Whereas distance modification was most extensive for the closer target, analysis of acceleration profiles revealed that, regardless of target position, visual information about start location determined the initial peak in tangential hand acceleration. Peak acceleration scaled with peak velocity and movement distance, a phenomenon termed “pulse-height” control. In contrast, proprioceptive information about actual hand location determined the duration of acceleration, which also scaled with peak velocity and movement distance, a phenomenon termed “pulse-width” control. Because pulse-height and pulse-width mechanisms reflect movement planning and sensory-based corrective processes, respectively, our current findings indicate that vision is used primarily for planning movement distance, while proprioception is used primarily for online corrections during rapid, unseen movements toward visual targets.     

Changes in head and neck position affect elbow joint position sense

Changes in the position of the head and neck have been shown to introduce a systematic deviation in the end-point error of an upper limb pointing task. Although previous authors have attributed this to alteration of perceived target location, no studies have explored the effect of changes in head and neck position on the perception of limb position. This study investigated whether changes in head and neck position affect a specific component of movement performance, that is, the accuracy of joint position sense (JPS) at the elbow. Elbow JPS was tested with the neck in four positions: neutral, flexion, rotation and combined flexion/rotation. A target angle was presented passively with the neck in neutral, after a rest period; this angle was reproduced actively with the head and neck in one of the test positions. The potential effects of distraction from head movement were controlled for by performing a movement control in which the head and neck were in neutral for the presentation and reproduction of the target angle, but moved into flexion during the rest period. The absolute and variable joint position errors (JPE) were greater when the target angle was reproduced with the neck in the flexion, rotation, and combined flexion/rotation than when the head and neck were in neutral. This study suggests that the reduced accuracy previously seen in pointing tasks with changes in head position may be partly because of errors in the interpretation of arm position.     

Eye-movements intervening between two successive sounds disrupt comparisons of auditory location

Many studies have investigated how saccades may affect the internal representation of visual locations across eye-movements. Here, we studied, instead, whether eye-movements can affect auditory spatial cognition. In two experiments, participants judged the relative azimuth (same/different) of two successive sounds presented from a horizontal array of loudspeakers, separated by a 2.5-s delay. Eye-position was either held constant throughout the trial (being directed in a fixed manner to the far left or right of the loudspeaker array) or had to be shifted to the opposite side of the array during the retention delay between the two sounds, after the first sound but before the second. Loudspeakers were either visible (Experiment 1) or occluded from sight (Experiment 2). In both cases, shifting eye-position during the silent delay-period affected auditory performance in thn the successive auditory comparison task, even though the auditory inputs to be judged were equivalent. Sensitivity (d′) for the auditory discrimination was disrupted, specifically when the second sound shifted in the opposite direction to the intervening eye-movement with respect to the first sound. These results indicate that eye-movements affect internal representation of auditory location.

Stimulus duration and repetition rate influence newborns' head orientation toward sound

Three experiments evaluated the effects of stimulus duration and repetition rate on newborns' head orientation responses. In Experiment 1, 28 infants turned toward a 20-sec continuous rattle sound but not toward 14- and 500-msec rattle sounds. Signal energy as a possible explanation for the infants' difficulty orienting toward brief sounds was explored in Experiment 2. Twenty neonates did not turn toward a single 90 dB, 14-msec rattle sound, although a longer duration (10 sec) sound containing less energy (70 dB) did elicit reliable head orientation. In Experiment 3, 16 neonates heard trains of repeated 14-msec rattle sounds (2/sec, 1.3/sec, and 1/sec) lasting 10 sec as well as a 10-sec continuous rattle sound. They turned toward the most rapidly repeating brief sound and the continuous one, while the slowly repeating sounds elicited little head movement in any direction. These results suggest that newborns' head orientation is selectively deficient for brief sounds, that the difficulty does not result from lessened energy in the brief sounds, and that the efficacy of repeated brief sounds depends upon their repetition rates.     

Early phase of spatial mismatch negativity is localized to a posterior “where” auditory pathway

The auditory mismatch negativity (MMN) is an event-related potential that reflects early processing of changes in acoustic stimulus features. Although the MMN has been well characterized by previous work, the number, roles, and anatomical locations of its cortical generators remain unresolved. Here, we report that the MMN elicited by occasional deviations in sound location is comprised of two temporally and anatomically distinct phases: an early phase with a generator posterior to auditory cortex and contralateral to the deviant stimulus, and a later phase with generators that are more frontal and bilaterally symmetric. The posterior location of the early-phase generator suggests the engagement of neurons within a putative “where” pathway for processing spatial auditory information.     

Auditory Detection of Motion Velocity in Humans: a Magnetoencephalographic Study

No HeadingSummary: To investigate the cerebral mechanisms of auditory detection of motion velocity in the human brain, neuromagnetic fields elicited by six moving sounds and one stationary sound were investigated with a whole-cortex magnetoencephalography (MEG) system. The stationary sound evoked only one clear response at a latency of 109±6 ms (first response, or M100), but the six moving sounds evoked two clear responses: an earlier response at a latency of 116±7 ms (M100) and a later response at a latency ranging from 180 to 760 ms (magnetic motion response, or MM). The latency and amplitude of the MM were inversely related to the velocity of the moving sounds (p<0.02). The magnetic source of MM was related to the velocity of the moving sounds (p<0.05). A dynamic neuromagnetic response, MM, was elicited by the moving sounds, which likely encoded the neural processing of auditory detection of motion velocity. A specific neural network that processes the motion velocity in the human brain probably includes the bilateral superior temporal cortices and the brainstem. The left posterior and lateral part of the auditory cortex may play a pivotal role in the auditory detection of motion velocity.We thank Dr. Paul Babyn for his help and suggestions in these experiments. This paper was prepared with the assistance of Prof. Sharon Nancekivell, medical editor, Guelph, Ontario, Canada. This study was partially supported by the Savoy Foundation (Research Grant 77227).     

Some further observations on the effects of unilateral cortical ablation on sound localization in the cat

Summary It has previously been shown that unilateral ablation of the whole auditory cortex in the cat disrupts the precedence effect, and also interferes with the ability of the normal animal to discriminate in the Y-maze between a single sound on one side and a double sound consisting of a signal on both left and right sides.The present work has confirmed these effects and has shown that both can be obtained with lesions confined to AI and AII The one-versus-two deficit has invariably been seen in all the animals studied, but a proportion of animals do not show the precedence effect deficit. It has been confirmed that the apparent success of some animals can be due to the training effect of the one-versus-two paradigm, as was proposed in the earlier paper; however it has also been shown that this cannot be the explanation in all cases.It has been demonstrated that cats are able to localize sounds behind them with some success; turning around in the start box to reverse right and left space is therefore a possible strategy for overcoming a unilateral deficit. However, even with the head fixed in the forward-facing position, one animal was still able to run well above chance. The size of the lesion does not appear to be a correlate of the performance level.This research was supported by The Science Research Council of Great Britain and the Sloan Foundation