Neural networks underlying endogenous and exogenous visual-spatial orienting

The orienting of visual-spatial attention is fundamental to most organisms and is controlled through external (exogenous) or internal (endogenous) processes. Exogenous orienting is considered to be reflexive and automatic, whereas endogenous orienting refers to the purposeful allocation of attentional resources to a predetermined location in space. Although behavioral, electrophysiological and lesion research in both primates and humans suggests that separate neural systems control these different modes of orienting, previous human neuroimaging studies have largely reported common neuronal substrates. Therefore, event-related FMRI (ER-FMRI) was used to independently examine different components of the orienting response including endogenous facilitation, exogenous facilitation and inhibition of return (IOR). In contrast to previous studies, endogenous versus exogenous facilitation resulted in widespread cortical activation including bilateral temporoparietal junction, bilateral superior temporal gyrus, right middle temporal gyrus, right frontal eye field and left intraparietal sulcus. Conversely, IOR compared to endogenous facilitation resulted in only a single focus of activation in the left superior temporal gyrus. These findings suggest that endogenous orienting activates a large cortical network to achieve internally generated shifts of attentional resources versus the automatic orienting that occurs with exogenous cues. However, similar networks may mediate endogenous orienting and IOR. The activation of the temporoparietal junction suggests that it is involved in more effortful processes, such as endogenous orienting, as well as in attentional reorienting and locating targets. Current results are discussed in terms of the functional development of the visual-spatial attentional system.     

Endogenous and exogenous attention shifts are mediated by the same large-scale neural network

Event-related fMRI was used to examine the neural basis of endogenous (top-down) and exogenous (bottom-up) spatial orienting. Shifts of attention were induced by central (endogenous) or peripheral (exogenous) cues. Reaction times on subsequently presented targets showed the expected pattern of facilitation and inhibition in both conditions. No difference in brain activity was observed when the two orienting conditions were contrasted with a liberal threshold, showing that both forms of orienting were mediated by the same neural network. Compared to within-block control trials, both endogenous and exogenous orienting activated a fronto-parietal network consisting of premotor cortex, posterior parietal cortex, medial frontal cortex and right inferior frontal cortex. Within these regions, equally strong activation was observed for both orienting conditions. It is concluded that endogenous and exogenous orienting are mediated by the same large-scale network of frontal and parietal brain areas.     

Self-efficacy and self-management after stroke: a systematic review

Purpose.?Specific increases of reaction times (RTs) were found in normal subjects, when endogenous spatial cues and targets were separated by the vertical visual meridian (VM) or by the vertical auditory (AM) meridian, when targets were either visual or auditory. The aim of this study was to assess if this effect could be attributed to longer RTs needed to shift activation between the hemispheres, or rather to different spatial maps underlying visual and auditory attention.

Method.?We tested the VM effect in deaf subjects. If the shifting of activation from one hemisphere to the other causes the increase in RTs, then no differences between normal and sensory disabled people should take place, as the incoming perceptual information in the residual modality uses the same neural pathways while crossing the vertical meridian. Conversely, if the vertical meridian effects are related to the spatial representation systems underlying endogenous orienting mechanisms, then the lack of the auditory perceptual system in deaf people may have determined different organization processes in the brain circuits, strongly affecting the orienting mechanisms of spatial attention.

Results.?Compared with a control group of hearing subjects, we found no evidence of the VM effect in deaf subjects.

Conclusions.?This finding, jointly with those of a previous experiment which showed no AM effect on blind subjects (Olivetti Belardinelli & Santangelo 2005) supports the idea of different spatial maps underlying visual and auditory attention, and suggests that their co-existence may induce interference effects in space processing, giving rise to the anisotropic representation of visual and auditory spaces, observed in normal subjects.     

Are vertical meridian effects due to audio-visual interference? A new confirmation with deaf subjects

Purpose. Specific increases of reaction times (RTs) were found in normal subjects, when endogenous spatial cues and targets were separated by the vertical visual meridian (VM) or by the vertical auditory (AM) meridian, when targets were either visual or auditory. The aim of this study was to assess if this effect could be attributed to longer RTs needed to shift activation between the hemispheres, or rather to different spatial maps underlying visual and auditory attention.

Method. We tested the VM effect in deaf subjects. If the shifting of activation from one hemisphere to the other causes the increase in RTs, then no differences between normal and sensory disabled people should take place, as the incoming perceptual information in the residual modality uses the same neural pathways while crossing the vertical meridian. Conversely, if the vertical meridian effects are related to the spatial representation systems underlying endogenous orienting mechanisms, then the lack of the auditory perceptual system in deaf people may have determined different organization processes in the brain circuits, strongly affecting the orienting mechanisms of spatial attention.

Results. Compared with a control group of hearing subjects, we found no evidence of the VM effect in deaf subjects.

Conclusions. This finding, jointly with those of a previous experiment which showed no AM effect on blind subjects (Olivetti Belardinelli & Santangelo 2005) supports the idea of different spatial maps underlying visual and auditory attention, and suggests that their co-existence may induce interference effects in space processing, giving rise to the anisotropic representation of visual and auditory spaces, observed in normal subjects.     

Segregated processing of auditory motion and auditory location: an ERP mapping study

Recent studies have revealed a distinct cortical network activated during the analysis of sounds' spatial properties. Whether common brain regions in this auditory where pathway are involved in both auditory motion and location processing is unresolved. We investigated this question with multichannel auditory evoked potentials (AEPs) in 11 subjects. Stimuli were binaural 500-ms white noise bursts. Interaural time differences (ITD) created the sensation of moving or stationary sounds within each auditory hemifield, and subjects discriminated either their position or direction of motion in a blocked design. Scalp potential distributions (AEP maps) differentiated electric field configurations across stimulus classes. The initial approximately 250-ms poststimulus yielded common topographies for both stimulus classes and hemifields. After approximately 250-ms, moving and stationary sounds engaged distinct cortical networks at two time periods, again with no differences observed between hemifields. The first ( approximately 250- to 350-ms poststimulus onset) was during stimulus presentation, and the second ( approximately 550- to 900-ms poststimulus onset) occurred after stimulus offset. Distributed linear inverse solutions of the maps over the 250- to 350-ms time period revealed not only bilateral inferior frontal activation for both types of auditory spatial processing, but also strong right inferior parietal activation in the case of auditory motion discrimination. During the later 550-to 900-ms time period, right inferior parietal and bilateral inferior frontal activity was again observed for moving sounds, whereas strong bilateral superior frontal activity was seen in the case of stationary sounds. Collectively, the evidence supports the existence of partly segregated networks within the auditory where pathway for auditory location and auditory motion processing.     

Towards a fronto-temporal neural network for the decoding of angry vocal expressions

Vocal expressions commonly elicit activity in superior temporal and inferior frontal cortices, indicating a distributed network to decode vocally expressed emotions. We examined the involvement of this fronto-temporal network for the decoding of angry voices during attention towards (explicit attention) or away from emotional cues in voices (implicit attention) based on a reanalysis of previous data (Frühholz, S., Ceravolo, L., Grandjean, D., 2012. Cerebral Cortex 22, 1107-1117). The general network revealed high interconnectivity of bilateral inferior frontal gyrus (IFG) to different bilateral voice-sensitive regions in mid and posterior superior temporal gyri. Right superior temporal gyrus (STG) regions showed connectivity to the left primary auditory cortex and secondary auditory cortex (AC) as well as to high-level auditory regions. This general network revealed differences in connectivity depending on the attentional focus. Explicit attention to angry voices revealed a specific right-left STG network connecting higher-level AC. During attention to a nonemotional vocal feature we also found a left-right STG network implicitly elicited by angry voices that also included low-level left AC. Furthermore, only during this implicit processing there was widespread interconnectivity between bilateral IFG and bilateral STG. This indicates that while implicit attention to angry voices recruits extended bilateral STG and IFG networks for the sensory and evaluative decoding of voices, explicit attention to angry voices solely involves a network of bilateral STG regions probably for the integrative recognition of emotional cues from voices.     

Cortical activation to auditory mismatch elicited by frequency deviant and complex novel sounds: a PET study

The analysis of auditory deviant events outside the focus of attention is a fundamental capacity of human information processing and has been studied in experiments on Mismatch Negativity (MMN) and the P3a component in evoked potential research. However, generators contributing to these components are still under discussion. Here we assessed cortical blood flow to auditory stimulation in three conditions. Six healthy subjects were presented with standard tones, frequency deviant tones (MMN condition), and complex novel sounds (Novelty condition), while attention was directed to a nondemanding visual task. Analysis of the MMN condition contrasted with thestandard condition revealed blood flow changes in the left and right superior temporal gyrus, right superior temporal sulcus and left inferior frontal gyrus. Complex novel sounds contrasted with the standard condition activated the left superior temporal gyrus and the left inferior and middle frontal gyrus. A small subcortical activation emerged in the left parahippocampal gyrus and an extended activation was found covering the right superior temporal gyrus. Novel sounds activated the right inferior frontal gyrus when controlling for deviance probability. In contrast to previous studies our results indicate a left hemisphere contribution to a frontotemporal network of auditory deviance processing. Our results provide further evidence for a contribution of the frontal cortex to the processing of auditory deviance outside the focus of directed attention.     

Neural mechanisms of top-down control during spatial and feature attention

Theories of visual selective attention posit that both spatial location and nonspatial stimulus features (e.g., color) are elementary dimensions on which top-down attentional control mechanisms can selectively influence visual processing. Neuropsychological and neuroimaging studies have demonstrated that regions of superior frontal and parietal cortex are critically involved in the control of visual-spatial attention. This frontoparietal control network has also been found to be activated when attention is oriented to nonspatial stimulus features (e.g., motion). To test the generality of the frontoparietal network in attentional control, we directly compared spatial and nonspatial attention in a cuing paradigm. Event-related fMRI methods permitted the isolation of attentional control activity during orienting to a location or to a nonspatial stimulus feature (color). Portions of the frontoparietal network were commonly activated to the spatial and nonspatial cues. However, direct statistical comparisons of cue-related activity revealed subregions of the frontoparietal network that were significantly more active during spatial than nonspatial orienting when all other stimulus, task, and attentional factors were equated. No regions of the frontal-parietal network were more active for nonspatial cues in comparison to spatial cues. These findings support models suggesting that subregions of the frontal-parietal network are highly specific for controlling spatial selective attention.     

Selective influences of cross-modal spatial-cues on preattentive auditory processing: a whole-head magnetoencephalography study

The processing streams of the various sensory modalities are known to interact within the central nervous system. These interactions differ depending on the level of stimulus representation and attention. The current study focused on cross-sensory influences on stimulus change detection during unattended auditory processing. We employed an oddball paradigm to assess cortical processing using whole-head magnetoencephalography (MEG) in 20 volunteers. While subjects performed distraction tasks of varying difficulties, auditory duration deviants were applied randomly to the left or the right ear preceded (200-400 ms) by oculomotor, static visual, or flow field co-stimulation at either side. Mismatch fields were recorded over both hemispheres. Changes in gaze direction and static visual stimuli elicited the most reliable enhancement of deviance detection at the same side (most prominent at the right auditory cortex). Under both conditions, the lateralized unattended and unpredictive pre-cues acted analogously to shifts in selective attention, but were not reduced by attentional load. Thus, the early cognitive representation of sounds seems to reflect automatic cross-modal interference. Preattentive multisensory integration may provide the neuronal basis for orienting reactions to objects in space and thus for voluntary control of selective attention.     

Cue validity modulates the neural correlates of covert endogenous orienting of attention in parietal and frontal cortex

Parietal brain regions have been implicated in reorienting of visuospatial attention in location-cueing paradigms when misleading advance information is provided in form of a spatially invalid cue. The difference in reaction times to invalidly and validly cued targets is termed the "validity effect" and used as a behavioral measure for attentional reorienting. Behavioral studies suggest that the magnitude of the validity effect depends on the ratio of validly to invalidly cued targets (termed cue validity), i.e., on the amount of top-down information provided. Using fMRI, we investigated the effects of a cue validity manipulation upon the neural mechanisms underlying attentional reorienting using valid and invalid spatial cues in the context of 90% and 60% cue validity, respectively. We hypothesized that increased parietal activation would be elicited when subjects need to reorient their attention in a context of high cue validity. Behaviorally, subjects showed significantly higher validity effects in the high as compared to the low cue validity condition, indicating slower reorienting. The neuroimaging data revealed higher activation of right inferior parietal and right frontal cortex in the 90% than in the 60% cue validity condition. We conclude that the amount of top-down information provided by predictive cues influences the neural correlates of reorienting of visuospatial attention by modulating activation of a right fronto-parietal attentional network.     

Automatic attention orienting by social and symbolic cues activates different neural networks: an fMRI study

Visual attention can be automatically re-oriented by another person's non-predictive gaze as well as by symbolic arrow cues. We investigated whether the shifts of attention triggered by biologically relevant gaze cues and biologically non-relevant arrow cues rely on the same neural systems by comparing the effects of gaze-cued and arrow-cued orienting on blood oxygenation level-dependent (BOLD) signal in humans. Participants detected laterally presented reaction signals preceded by centrally presented non-predictive gaze and arrow cues. Directional gaze cues and arrow cues were presented in separate blocks. Furthermore, two separate control blocks were run in which non-directional cues (straight gaze or segment of a line) were used. The BOLD signals during the control blocks were subtracted from those during the respective blocks with directional cues. Behavioral data showed that, for both cue types, reaction times were shorter on congruent than incongruent trials. Imaging data revealed three foci of activation for gaze-cued orienting: in the left inferior occipital gyrus and right medial and inferior occipital gyri. For arrow-cued orienting, a much more extensive network was activated. There were large postcentral activations bilaterally including areas in the medial/inferior occipital gyri and medial temporal gyri and in the left intraparietal area. Interestingly, arrow cuing also activated the right frontal eye field and supplementary eye field. The results suggest that attention orienting by gaze cues and attention orienting by arrow cues are not supported by the same cortical network and that attention orienting by symbolic arrow cues relies on mechanisms associated with voluntary shifts of attention.     

A parietal-frontal network studied by somatosensory oddball MEG responses, and its cross-modal consistency

Previous studies using functional magnetic resonance imaging (fMRI) and event-related potentials (ERPs) of the brain have found that a distributed parietal-frontal neuronal network is activated in normals during both auditory and visual oddball tasks. The common cortical regions in this network are inferior parietal lobule (IPL)/supramarginal gyrus (SMG), anterior cingulate cortex (ACC), and dorsolateral prefrontal cortex (DLPFC). It is not clear whether the same network is activated by oddball tasks during somatosensory stimulation. The present study addressed this question by testing healthy adults as they performed a novel median-nerve oddball paradigm while undergoing magnetoencephalography (MEG). An automated multiple dipole analysis technique, the Multi-Start Spatio-Temporal (MSST) algorithm, localized multiple neuronal generators, and identified their time-courses. IPL/SMG, ACC, and DLPFC were reliably localized in the MEG median-nerve oddball responses, with IPL/SMG activation significantly preceding ACC and DLPFC activation. Thus, the same parietal-frontal neuronal network that shows activation during auditory and visual oddball tests is activated in a median-nerve oddball paradigm. Regions uniquely related to somatosensory oddball responses (e.g., primary and secondary somatosensory, dorsal premotor, primary motor, and supplementary motor areas) were also localized. Since the parietal-frontal network supports attentional allocation during performance of the task, this study may provide a novel method, as well as normative baseline data, for examining attention-related deficits in the somatosensory system of patients with neurological or psychiatric disorders.     

Assessing the auditory dual-pathway model in humans

Evidence from anatomical and neurophysiological studies in nonhuman primates suggests a dual-pathway model of auditory processing wherein sound identity and sound location information are segregated along ventral and dorsal streams, respectively. The present meta-analysis reviewed evidence from auditory functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) studies to determine the reliability of this model in humans. Activation coordinates from 11 "spatial" studies (i.e., listeners made localization judgements on sounds that could occur at two or more perceptually different positions) and 27 "nonspatial" studies (i.e., listeners completed nonspatial tasks involving sounds presented from the same location) were entered into the analysis. All but one of the spatial studies reported activation within the inferior parietal lobule as opposed to only 41% of the nonspatial studies. In addition, 55% of spatial studies reported activity around the superior frontal sulcus as opposed to only 7% of the nonspatial studies. In comparison, inferior frontal activity (Brodmann's areas 45 and 47) was reported in only 9% of the spatial studies, but in 56% of the nonspatial studies. Finally, almost all temporal lobe activity observed during spatial tasks was confined to posterior areas, whereas nonspatial activity was distributed throughout the temporal lobe. These results support an auditory dual-pathway model in humans in which nonspatial sound information (e.g., sound identity) is processed primarily along the ventral stream whereas sound location is processed along the dorsal stream and areas posterior to primary auditory cortex.     

Neuroanatomical dissociation between bottom-up and top-down processes of visuospatial selective attention

Allocation of attentional resources to portions of the available sensory input can be regulated by bottom-up processes, i.e., spontaneous orientation towards an oncoming stimulus (stimulus-driven attention), and by top-down processes, i.e., intentionally and driven by knowledge, expectation and goals. The present study aimed at advancing the understanding of brain networks mediating bottom-up and top-down control of visuospatial attention by employing a paradigm that parametrically varied demands on these two processes. Spatial predictability of peripheral targets was parametrically varied by centrally cueing one, two, three or four of four possible locations. Reaction time decreased linearly with more precise valid cueing of the target location and increased with more precise invalid cueing. Event-related functional magnetic resonance imaging (fMRI) enabled measurement of blood oxygenation level-dependent (BOLD) responses to cues and to targets. A mostly left-hemispheric network consisting of left intraparietal sulcus, inferior and superior parietal lobule, bilateral precuneus, middle frontal gyri including superior frontal sulci, and middle occipital gyri displayed BOLD responses to cues that increased linearly with more precise spatial cueing, indicating engagement by top-down spatial selective attention. In contrast, bilateral temporoparietal junction, cingulate gyrus, right precentral gyrus and anterior and posterior insula, bilateral fusiform gyri, lingual gyri and cuneus displayed BOLD responses to targets that increased with their spatial unpredictability, indicating engagement by stimulus-driven orienting. The results suggest two largely dissociated neural networks mediating top-down and bottom-up control of visuospatial selective attention.     

How efficient is the orienting of spatial attention to pain? An experimental investigation

This study investigated how efficient spatial attention was oriented to pain in 2 experiments. Participants detected whether painful (pain group) or nonpainful (control group) somatosensory stimuli were delivered to the left or right hand. Each stimulus was preceded by a visual cue presented near to the stimulated hand (valid trial), the opposite hand (invalid trial), or centrally between hands. To examine both exogenous and endogenous orienting of attention, the spatial predictability of somatosensory targets was manipulated. In the first experiment, visual cues were nonpredictive for the location of the pain stimulus, as a result of which, orienting was purely exogenous, i.e., resulting from the occurrence of the visual cue at the location of somatosensory input. In the second experiment, visual cues were spatially predictive, as a result of which, endogenous control was added, i.e., attention driven by expectations of where the somatosensory target will occur. The results showed that only in experiment 1 was spatial attention oriented more efficiently to painful compared with nonpainful somatosensory stimulation. This effect was due to faster responses on valid relative to baseline trials (engagement), rather than slower responses on invalid relative to baseline trials (disengagement), and was significantly correlated with self-reported bodily threat. In experiment 2, prioritization of the pain location was probably overridden by task strategies because it was advantageous for participants' task performance to attend to the cued location irrespective of whether stimulation was painful or not. Implications of these findings for theories of hypervigilance and attentional management of pain are discussed.     

Functional segregation of the temporal lobes into highly differentiated subsystems for auditory perception: an auditory rapid event-related fMRI-task

With this study, we explored the blood oxygen level-dependent responses within the temporal lobe to short auditory stimuli of different classes. To address this issue, we performed an attentive listening event-related fMRI study, where subjects were required to concentrate during the presentation of different types of stimuli. Because the order of stimuli was randomized and not predictable for the subject, the observed differences between the stimuli types were interpreted as an automatic effect and were not affected by attention. We used three types of stimuli: tones, sounds of animals and instruments, and words. We found in all cases bilateral activations of the primary and secondary auditory cortex. The strength and lateralization depended on the type of stimulus. The tone trials led to the weakest and smallest activations. The perception of sounds increased the activated network bilaterally into the superior temporal sulcus mainly on the right and the perception of words led to the highest activation within the left superior temporal sulcus as well as in left inferior frontal gyrus. Within the left temporal sulcus, we were able to distinguish between different subsystems, showing an extending activation from posterior to anterior for speech and speechlike information. Whereas posterior parts were involved in analyzing the complex auditory structure of sounds and speech, the middle and anterior parts responded strongest only in the perception of speech. In summary, a functional segregation of the temporal lobes into several subsystems responsible for auditory processing was visible. A lateralization for verbal stimuli to the left and sounds to the right was already detectable when short stimuli were used.     

Control networks and hemispheric asymmetries in parietal cortex during attentional orienting in different spatial reference frames

Neuropsychological research has consistently demonstrated that spatial attention can be anchored in one of several coordinate systems, including those defined with respect to an observer (viewer-centered), to the gravitational vector (environment-centered), or to individual objects (object-centered). In the present study, we used hemodynamic correlates of brain function to investigate the neural systems that mediate attentional control in two competing reference frames. Healthy volunteers were cued to locations defined in either viewer-centered or object-centered space to discriminate the shape of visual targets subsequently presented at the cued locations. Brain responses to attention-directing cues were quantified using event-related functional magnetic resonance imaging. A fronto-parietal control network was activated by attention-directing cues in both reference frames. Voluntary shifts of attention produced increased neural activity bilaterally in several cortical regions including the intraparietal sulcus, anterior cingulate cortex, and the frontal eye fields. Of special interest was the observation of hemispheric asymmetries in parietal cortex; there was significantly greater activity in left parietal cortex than in the right, but this asymmetry was more pronounced for object-centered shifts of attention, relative to viewer-centered shifts of attention. Measures of behavioral performance did not differ significantly between the two reference frames. We conclude that a largely overlapping, bilateral, cortical network mediates our ability to orient spatial attention in multiple coordinate systems, and that the left intraparietal sulcus plays an additional role for orienting in object-centered space. These results provide neuroimaging support for related claims based on findings of deficits in object-based orienting in patients with left parietal lesions.     

Atypical neural networks for social orienting in autism spectrum disorders

Autism spectrum disorders (ASD) are characterized by significant social impairments, including deficits in orienting attention following social cues. Behavioral studies investigating social orienting in ASD, however, have yielded mixed results, as the use of naturalistic paradigms typically reveals clear deficits whereas computerized laboratory experiments often report normative behavior. The present study is the first to examine the neural mechanisms underlying social orienting in ASD in order to provide new insight into the social attention impairments that characterize this disorder. Using fMRI, we examined the neural correlates of social orienting in children and adolescents with ASD and in a matched sample of typically developing (TD) controls while they performed a spatial cueing paradigm with social (eye gaze) and nonsocial (arrow) cues. Cues were either directional (indicating left or right) or neutral (indicating no direction), and directional cues were uninformative of the upcoming target location in order to engage automatic processes by minimizing expectations. Behavioral results demonstrated intact orienting effects for social and nonsocial cues, with no differences between groups. The imaging results, however, revealed clear group differences in brain activity. When attention was directed by social cues compared to nonsocial cues, the TD group showed increased activity in frontoparietal attention networks, visual processing regions, and the striatum, whereas the ASD group only showed increased activity in the superior parietal lobule. Significant group × cue type interactions confirmed greater responsivity in task-relevant networks for social cues than nonsocial cues in TD as compared to ASD, despite similar behavioral performance. These results indicate that, in the autistic brain, social cues are not assigned the same privileged status as they are in the typically developing brain. These findings provide the first empirical evidence that the neural circuitry involved in social orienting is disrupted in ASD and highlight that normative behavioral performance in a laboratory setting may reflect compensatory mechanisms rather than intact social attention.     

Placing a tool in the spotlight: spatial attention modulates visuomotor responses in cortex

Visual spatial attention has long been associated with facilitatory effects on visual perception. Here, we report that spatial attention can also modulate implicit visuomotor processing in dorsal regions of human cortex. Participants underwent fMRI scanning while performing a voluntary attentional orienting task that varied the category of a task-irrelevant object in the attended location (tool vs. non-tool). Data were then analyzed as a function of the attended location (left vs. right visual field) and the object category in that location. We found that the fMRI BOLD response in two visuomotor-related regions--the supplementary motor area (SMA) and the left inferior parietal lobule (IPL)--showed an interaction between the location of attention and the location of the tool in the bilateral display. Further, these responses were statistically distinct from those regions in dorsal cortex showing activity modulated only by the tool location or only by the attended location. While the effects of attending non-foveally within the visual field have been well documented in relation to visual perception, our findings support the proposal that voluntary visuospatial attention may also have consequences for the implicit planning of object-directed actions.     

Where sound position influences sound object representations: a 7-T fMRI study

Evidence from human and non-human primate studies supports a dual-pathway model of audition, with partially segregated cortical networks for sound recognition and sound localisation, referred to as the What and Where processing streams. In normal subjects, these two networks overlap partially on the supra-temporal plane, suggesting that some early-stage auditory areas are involved in processing of either auditory feature alone or of both. Using high-resolution 7-T fMRI we have investigated the influence of positional information on sound object representations by comparing activation patterns to environmental sounds lateralised to the right or left ear. While unilaterally presented sounds induced bilateral activation, small clusters in specific non-primary auditory areas were significantly more activated by contra-laterally presented stimuli. Comparison of these data with histologically identified non-primary auditory areas suggests that the coding of sound objects within early-stage auditory areas lateral and posterior to primary auditory cortex AI is modulated by the position of the sound, while that within anterior areas is not.