Biomedical subjects

John J Foxe

Publications and source records attributed to John J Foxe.

At least 19 recordsLinked to original sources

PubMed2006

Do you see what I am saying? Exploring visual enhancement of speech comprehension in noisy environments.

Viewing a speaker's articulatory movements substantially improves a listener's ability to understand spoken words, especially under noisy environmental conditions. It has been claimed that this gain is most pronounced when auditory input is weakest, an effect that has been related to a well-known principle of multisensory integration--"inverse effectiveness." In keeping with the predictions of this principle, the present study showed substantial gain in multisensory speech enhancement at even the lowest signal-to-noise ratios (SNRs) used (-24 dB), but it was also evident that there was a "special zone" at a more intermediate SNR of -12 dB where multisensory integration was additionally enhanced beyond the predictions of this principle. As such, we show that inverse effectiveness does not strictly apply to the multisensory enhancements seen during audiovisual speech perception. Rather, the gain from viewing visual articulations is maximal at intermediate SNRs, well above the lowest auditory SNR where the recognition of whole words is significantly different from zero. We contend that the multisensory speech system is maximally tuned for SNRs between extremes, where the system relies on either the visual (speech-reading) or the auditory modality alone, forming a window of maximal integration at intermediate SNR levels. At these intermediate levels, the extent of multisensory enhancement of speech recognition is considerable, amounting to more than a 3-fold performance improvement relative to an auditory-alone condition.

Adolescent↗

PubMed2006

Seeing voices: High-density electrical mapping and source-analysis of the multisensory mismatch negativity evoked during the McGurk illusion.

Seeing a speaker's facial articulatory gestures powerfully affects speech perception, helping us overcome noisy acoustical environments. One particularly dramatic illustration of visual influences on speech perception is the "McGurk illusion", where dubbing an auditory phoneme onto video of an incongruent articulatory movement can often lead to illusory auditory percepts. This illusion is so strong that even in the absence of any real change in auditory stimulation, it activates the automatic auditory change-detection system, as indexed by the mismatch negativity (MMN) component of the auditory event-related potential (ERP). We investigated the putative left hemispheric dominance of McGurk-MMN using high-density ERPs in an oddball paradigm. Topographic mapping of the initial McGurk-MMN response showed a highly lateralized left hemisphere distribution, beginning at 175 ms. Subsequently, scalp activity was also observed over bilateral fronto-central scalp with a maximal amplitude at approximately 290 ms, suggesting later recruitment of right temporal cortices. Strong left hemisphere dominance was again observed during the last phase of the McGurk-MMN waveform (350-400 ms). Source analysis indicated bilateral sources in the temporal lobe just posterior to primary auditory cortex. While a single source in the right superior temporal gyrus (STG) accounted for the right hemisphere activity, two separate sources were required, one in the left transverse gyrus and the other in STG, to account for left hemisphere activity. These findings support the notion that visually driven multisensory illusory phonetic percepts produce an auditory-MMN cortical response and that left hemisphere temporal cortex plays a crucial role in this process.

Acoustic Stimulation↗

PubMed2006

Audio-visual multisensory integration in superior parietal lobule revealed by human intracranial recordings.

Intracranial recordings from three human subjects provide the first direct electrophysiological evidence for audio-visual multisensory processing in the human superior parietal lobule (SPL). Auditory and visual sensory inputs project to the same highly localized region of the parietal cortex with auditory inputs arriving considerably earlier (30 ms) than visual inputs (75 ms). Multisensory integration processes in this region were assessed by comparing the response to simultaneous audio-visual stimulation with the algebraic sum of responses to the constituent auditory and visual unisensory stimulus conditions. Significant integration effects were seen with almost identical morphology across the three subjects, beginning between 120 and 160 ms. These results are discussed in the context of the role of SPL in supramodal spatial attention and sensory-motor transformations.

Acoustic Stimulation↗

PubMed2006

The anterior cingulate and error avoidance.

The precise role of the anterior cingulate cortex in monitoring, evaluating, and correcting behavior remains unclear despite numerous theories and much empirical data implicating it in cognitive control. The present event-related functional magnetic resonance imaging study was able to separate monitoring from error-specific functions by allowing subjects to reject a trial so as to avoid errors. Cingulate and left dorsolateral prefrontal activity was greatest on rejection trials but comparable for correct and error trials, whereas an error-specific response was observed in bilateral insula. A dissociation was also observed between the cingulate and the nucleus accumbens with the latter more active for error than reject trials. These results reveal that the functional role of the cingulate is not particular to errors but instead is related to an evaluative function concerned with on-line behavioral adjustment in the service of avoiding losses.

Adult↗

PubMed2006

Changing plans: neural correlates of executive control in monkey and human frontal cortex.

Changing plans depends on executive control, the orchestration of behavior based on knowledge of both goal and context. Dorsolateral prefrontal (DLPFC) and anterior cingulate (ACC) cortices are clearly involved in these processes. Intracranial recordings in these regions were obtained from a monkey performing an executive control-challenging task that is widely used in clinic and laboratory to assess the integrity of cognitive function, the AX version of the continuous performance task (AX-CPT), and directly compared to scalp-recorded evoked potentials in humans. In this task the subject presses a button when detecting a frequent cue-target probe sequence in a stream of letters presented on a computer screen, and withholds response following incorrect sequences. Thus correct performance requires correct encoding of cue and probe instruction and inhibitory control. Intracranial recordings showed that DLPFC in the monkey was primarily activated by conditions that required inhibition of imminent action, as had been shown in human event-related potential (ERP) recordings. Different subregions of monkey ACC were activated primarily by either initiating or inhibiting action, whereas human ERP had shown ACC activation in both situations. We suggest that simultaneous activation of both types of subregions in conflict conditions may account the ubiquitous ACC activation observed with fMRI and ERP in those conditions.

Animals↗

PubMed2006

Increases in alpha oscillatory power reflect an active retinotopic mechanism for distracter suppression during sustained visuospatial attention.

Human electrophysiological (EEG) studies have demonstrated the involvement of alpha band (8- to 14-Hz) oscillations in the anticipatory biasing of attention. In the context of visual spatial attention within bilateral stimulus arrays, alpha has exhibited greater amplitude over parietooccipital cortex contralateral to the hemifield required to be ignored, relative to that measured when the same hemifield is to be attended. Whether this differential effect arises solely from alpha desynchronization (decreases) over the "attending" hemisphere, from synchronization (increases) over the "ignoring" hemisphere, or both, has not been fully resolved. This is because of the confounding effect of externally evoked desynchronization that occurs involuntarily in response to visual cues. Here, bilateral flickering stimuli were presented simultaneously and continuously over entire trial blocks, such that externally evoked alpha desynchronization is equated in precue baseline and postcue intervals. Equivalent random letter sequences were superimposed on the left and right flicker stimuli. Subjects were required to count the presentations of the target letter "X" at the cued hemifield over an 8-s period and ignore the sequence in the opposite hemifield. The data showed significant increases in alpha power over the ignoring hemisphere relative to the precue baseline, observable for both cue directions. A strong attentional bias necessitated by the subjective difficulty in gating the distracting letter sequence is reflected in a large effect size of 2.1 (eta2 = 0.82), measured from the attention x hemisphere interaction. This strongly suggests that alpha synchronization reflects an active attentional suppression mechanism, rather than a passive one reflecting "idling" circuits.

Adult↗

PubMed2006

Flexible cognitive control: effects of individual differences and brief practice on a complex cognitive task.

Brain activations underlying cognitive processes are subject to modulation as a result of increasing cognitive demands, individual differences, and practice. The present study investigated these modulatory effects in a cognitive control task which required inhibition of prepotent responses based on the contents of working memory (WM) and which enabled a novel dissociation of item-specific and task-skill effects resulting from brief practice. Distinct responses in areas underlying WM and inhibitory control in the absence of behavioral changes reflected different effects of item repetition and general task practice on tonic working memory and phasic inhibitory processes. Item repetition was associated with decreases in both unique and common areas subserving WM and inhibitory control. In contrast, general task practice was reflected in decreases in the level of tonic WM activity required to maintain a consistently high level of task performance but increased activity in a number of core inhibitory regions including dorsolateral and inferior PFC and inferior parietal cortex. Furthermore, both practice and individual differences in task performance were associated with the ability to modulate and maintain activity in frontostriatal areas mediating attentional control, suggesting that the areas that differ between individuals can be modulated by practice within an individual. These results raise the possibility that a fundamental human ability, reflexive cognitive control, is amenable to practice.

Adolescent↗

PubMed2006

Mapping the functional anatomy of task preparation: priming task-appropriate brain networks.

The present study used functional magnetic resonance imaging (fMRI) and a cued version of a flanker paradigm to elucidate the effects of task preparation on subsequent brain activation patterns. A mixed block and event-related design was employed to examine activations associated with the cue periods themselves and the cued and un-cued correct responses to incongruent flankers. A number of areas were active during the cues, most notably left dorsolateral prefrontal cortex (DLPFC), which was interpreted as subserving a role in task-set maintenance. Widespread activity was noted for correct responses to incongruent flankers, including bilateral parietal and frontal regions, consistent with previous studies. Activation was increased in these regions for correct responses after cue periods. An overlapping network of regions was also noted for cues and correct responses, suggesting preparation of task-appropriate anatomical regions during the cue period. These results suggest that cue periods allow participants to prime task-relevant areas within the brain and highlight the importance of left DLPFC in top-down control.

Adolescent↗

PubMed2005

Oscillatory beta activity predicts response speed during a multisensory audiovisual reaction time task: a high-density electrical mapping study.

Bisensory redundant targets are processed faster than the respective unisensory target stimuli alone as evidenced by substantially faster reaction times (RTs). This multisensory RT facilitation has been interpreted as an expression of integrative processing between the different sensory modalities. However, the neuronal mechanisms underlying the RT facilitation effect are not well understood. Oscillatory responses in the beta frequency range (13-30 Hz) have been related to sensory-motor processing. Here, we investigated whether modulation of beta responses might also underlie the faster RTs seen for multisensory stimuli. Using high-density electrical mapping, we explored the association between early (50-170 ms) multisensory processing in the evoked beta response and RTs recorded during a simple RT task. Subjects were instructed to indicate the appearance of any stimulus in a stream of auditory-alone (A), visual-alone (V), and multisensory (AV) stimuli by a button press. Beta responses were analyzed using Morlet wavelet transformations. Multisensory interactions were found over frontal, occipital, central, and sensory-motor regions. Critically, beta activity correlated with mean RTs over all stimulus types. Significant negative correlations were found for frontal, occipital, and sensory-motor scalp regions. We conclude that the association between oscillatory beta activity and integrative multisensory processing is directly linked to multisensory RT facilitation effects.

Acoustic Stimulation↗

PubMed2005

Spatiotemporal dynamics of human object recognition processing: an integrated high-density electrical mapping and functional imaging study of "closure" processes.

Humans are capable of recognizing objects, often despite highly adverse viewing conditions (e.g., occlusion). The term "perceptual closure" has been used to refer to the neural processes responsible for "filling-in" missing information in the visual image under such conditions. Closure phenomena have been linked to a group of object recognition areas, the so-called lateral-occipital complex (LOC). Here, we investigated the spatiotemporal dynamics of perceptual closure processes by coregistering data from high-density electrical recordings (ERPs) and functional magnetic resonance imaging (fMRI) while subjects participated in a perceptual closure task. Subjects were presented with highly fragmented images and control scrambled images. Fragmented images were calibrated to be 'just' recognizable as objects (that is, perceptual closure was necessary), whereas the scrambled images were unrecognizable. Comparison of responses to these two stimulus classes revealed the neural processes underlying perceptual closure. fMRI revealed an object recognition system that mediates these closure processes, the core of which consists of the LOC regions. ERP recordings resulted in the well-characterized N(CL) component (for negativity associated with closure), a robust relative negativity over bilateral occipito-temporal scalp that occurs in the 230-400 ms timeframe. Our investigations further revealed an extended network of dorsal and frontal regions, also involved in perceptual closure processes. Inverse source analysis showed that the major generators of N(CL) localized to the identical regions within LOC revealed by the fMRI recordings and detailed the temporal dynamics across these LOC regions including interactions between LOC and these other nodes of the object recognition circuit.

Adult↗

PubMed2005

The brain uses single-trial multisensory memories to discriminate without awareness.

Multisensory experiences enhance perceptions and facilitate memory retrieval processes, even when only unisensory information is available for accessing such memories. Using fMRI, we identified human brain regions involved in discriminating visual stimuli according to past multisensory vs. unisensory experiences. Subjects performed a completely orthogonal task, discriminating repeated from initial image presentations intermixed within a continuous recognition task. Half of initial presentations were multisensory, and all repetitions were exclusively visual. Despite only single-trial exposures to initial image presentations, accuracy in indicating image repetitions was significantly improved by past auditory-visual multisensory experiences over images only encountered visually. Similarly, regions within the lateral-occipital complex-areas typically associated with visual object recognition processes-were more active to visual stimuli with multisensory than unisensory pasts. Additional differential responses were observed in the anterior cingulate and frontal cortices. Multisensory experiences are registered by the brain even when of no immediate behavioral relevance and can be used to categorize memories. These data reveal the functional efficacy of multisensory processing.

Acoustic Stimulation↗

PubMed2005

Biasing the brain's attentional set: II. effects of selective intersensory attentional deployments on subsequent sensory processing.

This study used high-density mapping of human event-related potentials to examine the brain activity associated with selective information processing when subjects were cued on a trial-by-trial basis to perform a discrimination in either the visual or auditory modality. On each trial, word-cues (S1) instructed subjects to attend to features within one sensory-modality of an impending compound auditory-visual stimulus (S2) that arrived approximately 1-second following the cue. Subjects made a discrimination within the cued modality of the S2 stimulus. The spatio-temporal patterns of activity in response to the compound S2 stimulus were examined as a function of the sensory modality being attended. The earliest effects of intersensory attention on visual processing were seen subsequent to the initial activation of visual cortex, beginning at 80 ms and continuing into the P1 and N1 components of the visual ERP. The scalp-topography of this earliest modulation was consistent with modulation of activity in ventral visual stream areas. Thus, the locus of effects on visual S2 processing differed from the anticipatory parieto-occipital biasing activity that preceded S2 presentation. This pattern of effects strongly suggests that the anticipatory activity (following the cue) associated with sustaining the focus of attention during intersensory attention, at least in the context of this paradigm, does not operate as a simple gain mechanism in early visual sensory areas. Rather, attentional biasing can operate through a higher-order process whereby parieto-occipital cortices influence the subsequent flow of visual processing in the ventral stream.

Acoustic Stimulation↗

PubMed2005

Biasing the brain's attentional set: I. cue driven deployments of intersensory selective attention.

Brain activity associated with directing attention to one of two possible sensory modalities was examined using high-density mapping of human event-related potentials. The deployment of selective attention was based on visually presented symbolic cue-words instructing subjects on a trial-by-trial basis, which sensory modality to attend. We measured the spatio-temporal pattern of activation in the approximately 1 second period between the cue-instruction and a subsequent compound auditory-visual imperative stimulus. This allowed us to assess the flow of processing across brain regions involved in deploying and sustaining inter-sensory selective attention, prior to the actual selective processing of the compound audio-visual target stimulus. Activity over frontal and parietal areas showed sensory specific increases in activation during the early part of the anticipatory period (~230 ms), probably representing the activation of fronto-parietal attentional deployment systems for top-down control of attention. In the later period preceding the arrival of the "to-be-attended" stimulus, sustained differential activity was seen over fronto-central regions and parieto-occipital regions, suggesting the maintenance of sensory-specific biased attentional states that would allow for subsequent selective processing. Although there was clear sensory biasing in this late sustained period, it was also clear that both sensory systems were being prepared during the cue-target period. These late sensory-specific biasing effects were also accompanied by sustained activations over frontal cortices that also showed both common and sensory specific activation patterns, suggesting that maintenance of the biased state includes top-down inputs from generators in frontal cortices, some of which are sensory-specific regions. These data support extensive interactions between sensory, parietal and frontal regions during processing of cue information, deployment of attention, and maintenance of the focus of attention in anticipation of impending attentionally relevant input.

Acoustic Stimulation↗

PubMed2005

How single-trial electrical neuroimaging contributes to multisensory research.

This study details a method to statistically determine, on a millisecond scale and for individual subjects, those brain areas whose activity differs between experimental conditions, using single-trial scalp-recorded EEG data. To do this, we non-invasively estimated local field potentials (LFPs) using the ELECTRA distributed inverse solution and applied non-parametric statistical tests at each brain voxel and for each time point. This yields a spatio-temporal activation pattern of differential brain responses. The method is illustrated here in the analysis of auditory-somatosensory (AS) multisensory interactions in four subjects. Differential multisensory responses were temporally and spatially consistent across individuals, with onset at approximately 50 ms and superposition within areas of the posterior superior temporal cortex that have traditionally been considered auditory in their function. The close agreement of these results with previous investigations of AS multisensory interactions suggests that the present approach constitutes a reliable method for studying multisensory processing with the temporal and spatial resolution required to elucidate several existing questions in this field. In particular, the present analyses permit a more direct comparison between human and animal studies of multisensory interactions and can be extended to examine correlation between electrophysiological phenomena and behavior.

Acoustic Stimulation↗

PubMed2005

Sensory contributions to impaired prosodic processing in schizophrenia.

BACKGROUND: Deficits in affect recognition are prominent features of schizophrenia. Within the auditory domain, patients show difficulty in interpreting vocal emotional cues based on intonation (prosody). The relationship of these symptoms to deficits in basic sensory processing has not been previously evaluated. METHODS: Forty-three patients and 34 healthy comparison subjects were tested on two affective prosody measures: voice emotion identification and voice emotion discrimination. Basic auditory sensory processing was measured using a tone-matching paradigm and the Distorted Tunes Test (DTT). A subset of subjects was also tested on facial affect identification and discrimination tasks. RESULTS: Patients showed significantly impaired performance on all emotion processing tasks. Within the patient group, a principal components analysis demonstrated significant intercorrelations between basic pitch perception and affective prosodic performance. In contrast, facial affect recognition deficits represented a distinct second component. Prosodic affect measures correlated significantly with severity of negative symptoms and impaired global outcome. CONCLUSIONS: These results demonstrate significant relationships between basic auditory processing deficits and impaired receptive prosody in schizophrenia. The separate loading of auditory and visual affective recognition measures suggests that within-modality factors may be more significant than cross-modality factors in the etiology of affect recognition deficits in schizophrenia.

Adult↗

PubMed2005

The case for feedforward multisensory convergence during early cortical processing.

The prevailing hierarchical model of sensory processing in the brain holds that different modalities of sensory information emanating from a single object are analyzed extensively during passage through their respective unisensory processing streams before they are combined in higher-order 'multisensory' regions of the cortex. Because of this view, multisensory interactions that have been found at early, putatively 'unisensory' cortical processing stages during hemodynamic imaging studies have been assumed to reflect feedback modulations that occur subsequent to multisensory processing in the higher-order multisensory areas. In this paper, we consider findings that challenge an exclusively feedback interpretation of early multisensory integration effects. First, high-density electrical mapping studies in humans have shown that multisensory convergence and integration effects can occur so early in the time course of sensory processing that purely feedback mediation becomes extremely unlikely. Second, direct neural recordings in monkeys show that, in some cases, convergent inputs at early cortical stages have physiological profiles characteristic of feedforward rather than feedback inputs. Third, damage to higher-order integrative regions in humans often spares the ability to integrate across sensory modalities. Finally, recent anatomic tracer studies have reported direct anatomical connections between primary visual and auditory cortex. These findings make it clear that multisensory convergence at early stages of cortical processing results from feedforward as well as feedback and lateral connections, thus using the full range of anatomical connections available in brain circuitry.

Animals↗

PubMed2005

Can whole brain nerve conduction velocity be derived from surface-recorded visual evoked potentials? A re-examination of Reed, Vernon, and Johnson (2004).

Reed, Vernon, and Johnson [Reed, T. E., Vernon, P. A., & Johnson, A. M. (2004). Sex difference in brain nerve conduction velocity in normal humans. Neuropsychologia, 42, 1709-1714] reported that "nerve conduction velocity" (NCV) of visual transmission from retina to the primary visual area (V1) is significantly faster in males than females. The authors estimated the NCV by dividing head length (nasion-to-inion distance) by the latency of the well-known P100 component of the visual evoked potential (VEP). Here, we critically examine these metrics and we contend that knowledge of the underlying physiology of neural transmission across the initial stages of the visual processing hierarchy dictates that a number of their assumptions cannot be reasonably upheld. Alternative, and we believe, more parsimonious interpretations of the data are also proposed.

Evoked Potentials, Visual↗

PubMed2005

Filling-in in schizophrenia: a high-density electrical mapping and source-analysis investigation of illusory contour processing.

Evidence is accumulating that patients with schizophrenia exhibit relatively severe deficits in early visual sensory processing within the dorsal stream, while processing within the ventral stream appears to be relatively more intact. Here, illusory contour (IC) processing was investigated in a cohort of schizophrenia patients and age-matched healthy controls using high-density visual evoked potentials (VEPs), spatiotemporal topographic analyses and the Local Auto-Regressive Average distributed linear inverse source estimation. IC processing was assessed because it is now known to be an excellent metric of early processing within regions of the ventral visual stream. Results in the present study show that IC processing (106-194 ms) is spared in patients with schizophrenia, providing strong evidence that early ventral stream processing is essentially normal. This is so despite equally strong evidence that early dorsal stream processing is severely impaired in this population, as indexed by a robust decrement in amplitude of the P1 component in patients and a large topographic difference between groups for this component (54-104 ms). Source analysis confirmed that the flow of activity into the dorsal stream was substantially decreased in patients. As such, these results suggest that some aspects of early ventral processing are not entirely reliant on intact inputs from the dorsal stream. Lastly, we show that later phases of visual processing (240-400 ms) also rely on the activity of different brain networks in controls and patients, with the latter recruiting strong frontal activity perhaps as compensation for impaired ventral stream processing during this period. We interpret the present findings in the context of a two-stage processing model. Under this model, it is suggested that the second stage of ventral stream processing is dependent on the fidelity of inputs from the dorsal visual stream and that impairment of this critical modulatory input may underlie the failure of 'higher-level' ventral stream processes in this population.

Adult↗