Jon Driver

The thing that should not be: predictive coding and the uncanny valley in perceiving human and humanoid robot actions.

Using functional magnetic resonance imaging (fMRI) repetition suppression, we explored the selectivity of the human action perception system (APS), which consists of temporal, parietal and frontal areas, for the appearance and/or motion of the perceived agent. Participants watched body movements of a human (biological appearance and movement), a robot (mechanical appearance and movement) or an android (biological appearance, mechanical movement). With the exception of extrastriate body area, which showed more suppression for human like appearance, the APS was not selective for appearance or motion per se. Instead, distinctive responses were found to the mismatch between appearance and motion: whereas suppression effects for the human and robot were similar to each other, they were stronger for the android, notably in bilateral anterior intraparietal sulcus, a key node in the APS. These results could reflect increased prediction error as the brain negotiates an agent that appears human, but does not move biologically, and help explain the ‘uncanny valley’ phenomenon.

Concurrent TMS-fMRI reveals dynamic interhemispheric influences of the right parietal cortex during exogenously cued visuospatial attention.

We used concurrent transcranial magnetic stimulation and functional MRI (TMS‐fMRI) during a visuospatial cueing paradigm in humans, to study the causal role of the right angular gyrus (AG) as a source of attentional control. Our findings show that TMS over the right AG (high vs. low intensity) modulates neural responses interhemispherically, in a manner that varies dynamically with the current attentional condition. The behavioural impact of such TMS depended not only on the target hemifield but also on exogenous cue validity, facilitating spatial reorienting to invalidly cued right visual targets. On a neural level, right AG TMS had corresponding interhemispheric effects in the left AG and left retinotopic cortex, including area V1. We conclude that the direction of covert visuospatial attention can involve dynamic interplay between the right AG and remote interconnected regions of the opposite left hemisphere, whereas our findings also suggest that the right AG can influence responses in the retinotopic visual cortex.

Local but not long-range microstructural differences of the ventral temporal cortex in developmental prosopagnosia

Individuals with developmental prosopagnosia (DP) experience face recognition impairments despite normal intellect and low-level vision and no history of brain damage. Prior studies using diffusion tensor imaging in small samples of subjects with DP (n=6 or n=8) offer conflicting views on the neurobiological bases for DP, with one suggesting white matter differences in two major long-range tracts running through the temporal cortex, and another suggesting white matter differences confined to fibers local to ventral temporal face-specific functional regions of interest (fROIs) in the fusiform gyrus. Here, we address these inconsistent findings using a comprehensive set of analyzes in a sample of DP subjects larger than both prior studies combined (n=16). While we found no microstructural differences in long-range tracts between DP and age-matched control participants, we found differences local to face-specific fROIs, and relationships between these microstructural measures with face recognition ability. We conclude that subtle differences in local rather than long-range tracts in the ventral temporal lobe are more likely associated with developmental prosopagnosia.

Mechanisms and anatomy of unilateral extinction after brain injury.

Unilateral extinction is a common consequence of unilateral brain injury in which individuals fail to detect a contralesional target when presented together with a competing ipsilesional target. Here we review the literature on the different mechanisms and anatomy hypothesized to underlie unilateral extinction. We argue that extinction, which reflects a specific deficit in the simultaneous processing of multiple briefly presented targets, should be distinguished from the failure to actively explore and serially detect targets amongst distractors in contralesional space commonly known as spatial neglect. While contralesional sensory defects can be correlated with extinction, these sensory impairments alone are usually not sufficient to explain the deficit. Prototypical extinction is instead best seen as the result of a pathologically biased competition between multiple target representations for pathologically limited attentional resources. The temporo-parietal junction (TPJ) is a critical site in many of the lesions that provoke extinction. Additionally, the intraparietal sulcus (IPS) may play a role in modulation of competitive interactions between multiple target representations.

Visual and Audiovisual Effects of Isochronous Timing on Visual Perception and Brain Activity

Understanding how the brain extracts and combines temporal structure (rhythm) information from events presented to different senses remains unresolved. Many neuroimaging beat perception studies have focused on the auditory domain and show the presence of a highly regular beat (isochrony) in “auditory” stimulus streams enhances neural responses in a distributed brain network and affects perceptual performance. Here, we acquired functional magnetic resonance imaging (fMRI) measurements of brain activity while healthy human participants performed a visual task on isochronous versus randomly timed “visual” streams, with or without concurrent task-irrelevant sounds. We found that visual detection of higher intensity oddball targets was better for isochronous than randomly timed streams, extending previous auditory findings to vision. The impact of isochrony on visual target sensitivity correlated positively with fMRI signal changes not only in visual cortex but also in auditory sensory cortex during audiovisual presentations. Visual isochrony activated a similar timing-related brain network to that previously found primarily in auditory beat perception work. Finally, activity in multisensory left posterior superior temporal sulcus increased specifically during concurrent isochronous audiovisual presentations. These results indicate that regular isochronous timing can modulate visual processing and this can also involve multisensory audiovisual brain mechanisms.

fMRI correlates of subjective reversals in ambiguous structure-from-motion.

We used fMRI to examine the neural correlates of subjective reversals for bistable structure-from-motion. We compared transparent random-dot kinematograms depicting either a cylinder rotating in depth or two flat surfaces translating in opposite directions at apparently different depths. For both such stimuli, the motion of dots on the different apparent depth planes typically appears to reverse direction periodically on prolonged viewing. Yet for cylindrical but not flat stimuli, such subjective reversals also coincide with apparent reversal of 3D rotation direction. We hypothesized that the lateral occipital complex (region LOC), sensitive to 3D form, might show greater event-related activity for subjective reversals of cylindrical than flat stimuli; conversely, motion-sensitive hMT+/V5 should respond in common to subjective reversals for either type of stimuli, as both are perceived as changes in planar motion. We obtained an event-related measure of neural activity associated with subjective reversals after first factoring out block-related differences between cylindrical versus flat stimuli (and thereby the associated low-level blocked stimulus differences). In support of our hypothesis, only the cylindrical stimuli produced reversal-related activity in contralateral human LOC. In contrast, the hMT+/V5 complex was activated alike by subjective reversals for both cylindrical and flat stimuli. Intriguingly, V1 also showed (contralateral) specificity for rotational reversals, suggesting a possible feedback influence from LOC. These results reveal specific neural correlates for subjective switches of 3D rotation versus translation, as distinct from subjective reversals in general.

Neural correlates of visual extinction or awareness in a series of patients with right temporoparietal damage.

Patients with visual extinction following right-hemisphere damage can typically detect left visual field stimulation when it is presented in isolation, but tend to miss this when it is paired with competing concurrent right visual stimulation. Some single-case studies have provided preliminary evidence that right visual cortex may show residual activation for contralesional, extinguished visual stimuli. Here we go beyond prior work by using individual retinotopic mapping and online eye-tracking during fMRI to study activity in stimulus-responsive retinotopic visual cortex for a case series of four extinction patients. We found consistent activation of retinotopic right visual cortex for bilateral visual stimulation that resulted in left extinction. This residual unconscious activation included areas V1 to V3 and was not due to inadvertent eye movements. We also provide further evidence for the emerging view that awareness may require activity of frontal and parietal regions well beyond visual cortex.

Functional connectivity between prefrontal and parietal cortex drives visuo-spatial attention shifts

ABSTRACT It is well established that the frontal eye‐fields (FEF) in the dorsal attention network (DAN) guide top‐down selective attention. In addition, converging evidence implies a causal role for the FEF in attention shifting, which is also known to recruit the ventral attention network (VAN) and fronto‐striatal regions. To investigate the causal influence of the FEF as (part of) a central hub between these networks, we applied thetaburst transcranial magnetic stimulation (TBS) off‐line, combined with functional magnetic resonance (fMRI) during a cued visuo‐spatial attention shifting paradigm. We found that TBS over the right FEF impaired performance on a visual discrimination task in both hemifields following attention shifts, while only left hemifield performance was affected when participants were cued to maintain the focus of attention. These effects recovered ca. 20 min post stimulation. Furthermore, particularly following attention shifts, TBS suppressed the neural signal in bilateral FEF, right inferior and superior parietal lobule (IPL/SPL) and bilateral supramarginal gyri (SMG). Immediately post stimulation, functional connectivity was impaired between right FEF and right SMG as well as right putamen. Importantly, the extent of decreased connectivity between right FEF and right SMG correlated with behavioural impairment following attention shifts. The main finding of this study demonstrates that influences from right FEF on SMG in the ventral attention network causally underly attention shifts, presumably by enabling disengagement from the current focus of attention. HIGHLIGHTSThetaburst stimulation to the right FEF temporarily impairs bilateral attention shifts.Lateralised behavioural deficits in the contralateral hemifield are observed when cued to maintain attention.These effects recover ca. 20 min post stimulation.During shifts, neural activity is suppressed following right FEF TBS in the dorsal attention network and supramarginal gyri.Influences from right FEF to SMG causally underlie attention shifts, presumably by enabling disengagement from current focus.

Response to comment on: Exp Brain Res. 2011 May 5th. Transcranial magnetic stimulation of macaque frontal eye fields decreases saccadic reaction time. Pierre Pouget PhD, Nicolas Wattiez MSc and Antoni Valero-Cabre MDPhD

Abstract(not available)