Kaoru Sekiyama

Body image as a visuomotor transformation device revealed in adaptation to reversed vision

People adapt with remarkable flexibility to reversal of the visual field caused by prism spectacles. With sufficient time, this adaptation restores visually guided behaviour and perceptual harmony between the visible and tactile worlds. Although it has been suggested that seeing ones own body is crucial for adaptation, the underlying mechanisms are unclear. Here we show that a new representation of visuomotor mapping with respect to the hands emerges in a month during adaptation to reversed vision. The subjects become bi-perceptual, or able to use both new and old representations. In a visual task designed to assess the new hand representation, subjects identified visually presented hands as left or right by matching the picture to the representation of their own hands. Functional magnetic resonance imaging showed brain activity in the left posterior frontal cortex (Brocas area) that was unique to the new hand representations of both hands, together with activation in the intraparietal sulcus and prefrontal cortex. The emergence of the new hand representation coincided with the adaptation of perceived location of visible objects in space. These results suggest that the hand representation operates as a visuomotor transformation device that provides an arm-centred frame of reference for space perception.

A 12-Week Physical and Cognitive Exercise Program Can Improve Cognitive Function and Neural Efficiency in Community-Dwelling Older Adults: A Randomized Controlled Trial

To investigate whether a 12‐week physical and cognitive exercise program can improve cognitive function and brain activation efficiency in community‐dwelling older adults.

Enhanced perception of various linguistic features by musicians: A cross-linguistic study

Two cross-linguistic experiments comparing musicians and non-musicians were performed in order to examine whether musicians have enhanced perception of specific acoustical features of speech in a second language (L2). These discrimination and identification experiments examined the perception of various speech features; namely, the timing and quality of Japanese consonants, and the quality of Dutch vowels. We found that musical experience was more strongly associated with discrimination performance rather than identification performance. The enhanced perception was observed not only with respect to L2, but also L1. It was most pronounced when tested with Japanese consonant timing. These findings suggest the following: 1) musicians exhibit enhanced early acoustical analysis of speech, 2) musical training does not equally enhance the perception of all acoustic features automatically, and 3) musicians may enjoy an advantage in the perception of acoustical features that are important in both language and music, such as pitch and timing.

Enhanced audiovisual integration with aging in speech perception: a heightened McGurk effect in older adults

Two experiments compared young and older adults in order to examine whether aging leads to a larger dependence on visual articulatory movements in auditory-visual speech perception. These experiments examined accuracy and response time in syllable identification for auditory-visual (AV) congruent and incongruent stimuli. There were also auditory-only (AO) and visual-only (VO) presentation modes. Data were analyzed only for participants with normal hearing. It was found that the older adults were more strongly influenced by visual speech than the younger ones for acoustically identical signal-to-noise ratios (SNRs) of auditory speech (Experiment 1). This was also confirmed when the SNRs of auditory speech were calibrated for the equivalent AO accuracy between the two age groups (Experiment 2). There were no aging-related differences in VO lipreading accuracy. Combined with response time data, this enhanced visual influence for the older adults was likely to be associated with an aging-related delay in auditory processing.

Adaptation to left-right reversed vision rapidly activates ipsilateral visual cortex in humans

The brain mechanisms of adaptation to visual transposition are of increasing interest, not only for research on sensory-motor coordination, but also for neuropsychological rehabilitation. Sugita [Nature 380 (1996) 523] found that after adaptation to left-right reversed vision for one and a half months, monkey V1 neurons responded to stimuli presented not only in the contralateral visual field, but also in the ipsilateral visual field. To identify the underlying neuronal mechanisms of adaptation to visual transposition, we conducted fMRI and behavioral experiments for which four adult human subjects wore left-right reversing goggles for 35/39 days, and investigated: (1) whether ipsilateral V1 activation can be induced in human adult subjects; (2) if yes, when the ipsilateral activity starts, and what kind of behavioral/psychological changes occur accompanying the ipsilateral activity; (3) whether other visual cortices also show an ipsilateral activity change. The results of behavioral experiments showed that visuomotor coordinative function and internal representation of peripersonal space rapidly adapted to the left-right reversed vision within the first or second week. Accompanying these behavioral changes, we found that both primary (V1) and extrastriate (MT/MST) visual cortex in human adults responded to visual stimuli presented in the ipsilateral visual field. In addition, the ipsilateral activity started much sooner than the one and a half months, which had been expected from the monkey neurophysiological study. The results of the present study serve as physiological evidence of large-scale, cross-hemisphere, cerebral plasticity that exists even in adult human brain.

Brain activation during visual working memory correlates with behavioral mobility performance in older adults.

Functional mobility and cognitive function often decline with age. We previously found that functional mobility as measured by the Timed Up and Go Test (TUG) was associated with cognitive performance for visually-encoded (i.e., for location and face) working memory (WM) in older adults. This suggests a common neural basis between TUG and visual WM. To elucidate this relationship further, the present study aimed to examine the neural basis for the WM-mobility association. In accordance with the well-known neural compensation model in aging, we hypothesized that “attentional” brain activation for easy WM would increase in participants with lower mobility. The data from 32 healthy older adults were analyzed, including brain activation during easy WM tasks via functional Magnetic Resonance Imaging (fMRI) and mobility performance via both TUG and a simple walking test. WM performance was significantly correlated with TUG but not with simple walking. Some prefrontal brain activations during WM were negatively correlated with TUG performance, while positive correlations were found in subcortical structures including the thalamus, putamen and cerebellum. Moreover, activation of the subcortical regions was significantly correlated with WM performance, with less activation for lower WM performers. These results indicate that older adults with lower mobility used more cortical (frontal) and fewer subcortical resources for easy WM tasks. To date, the frontal compensation has been proposed separately in the motor and cognitive domains, which have been assumed to compensate for dysfunction of the other brain areas; however, such dysfunction was less clear in previous studies. The present study observed such dysfunction as degraded activation associated with lower performance, which was found in the subcortical regions. We conclude that a common dysfunction—compensation activation pattern is likely the neural basis for the association between visual WM and functional mobility.

Strong biomechanical constraints on young children's mental imagery of hands

Mental rotation (MR) of body parts is a useful paradigm to investigate how people manipulate mental imagery related to body schema. It has been documented that adult participants use ‘motor imagery’ for MR of hands: a behavioural indication is a biomechanical effect, that is, hand pictures in orientations to which imitative hand movement would be biomechanically difficult require longer response times to be visually identified as the left or right hand. However, little is known about the typical developmental trajectory of the biomechanical effect, which could offer clues to understanding how children acquire the ability to manipulate body schema. This study investigated developmental changes in the biomechanical effect in schoolchildren. Eighty-four children (from 6 to 11 years old, grouped into 1st, 2nd, 3rd, 4th and 5th graders) and fifteen adults made hand laterality judgements in an MR paradigm. The results indicated that the biomechanical effect is stronger for younger children, and that there is a transitional period (around 7–8 years) during which children shift from action execution to imagery in manipulating body schema. The results suggest that mental imagery of hands has a stronger motor aspect in the transitional period than later in childhood and adulthood.

Audiotactile interactions beyond the space and body parts around the head

Recent research has reported that spatial modulation effects of audiotactile interactions tend to be limited to the space and body parts around the head. The present study investigated the generality of this finding by manipulating body parts stimulated and spatial relationships between the body parts and sounds. In Experiment 1, tactile stimuli were presented randomly to either left or right cheek, hand (palm or back) placed near the head, and knee while auditory stimuli were presented to either the same or opposite side from loudspeakers close to the head. Participants made speeded spatial discrimination responses regarding the side (left versus right) of the tactile stimulation. For any body part stimulated, the performance was worse when the auditory stimuli were presented from the opposite side rather than from the same side. Experiment 2 demonstrated that the spatial modulation effects for the palm or the back of the hand occurred irrespective of hand position (near or far from the head) and sound position (near or far from the head). The sounds delivered from near the head exerted a greater influence on tactile spatial discrimination performance as compared with the sound delivered from far from the head. Furthermore, the back of the hand was more influenced by the auditory stimuli than the palm when the hands were placed near the sounds. These results suggest that the spatial modulation effects of audiotactile interactions can occur beyond the space and body surface around the head.

Language/Culture Modulates Brain and Gaze Processes in Audiovisual Speech Perception

Several behavioural studies have shown that the interplay between voice and face information in audiovisual speech perception is not universal. Native English speakers (ESs) are influenced by visual mouth movement to a greater degree than native Japanese speakers (JSs) when listening to speech. However, the biological basis of these group differences is unknown. Here, we demonstrate the time-varying processes of group differences in terms of event-related brain potentials (ERP) and eye gaze for audiovisual and audio-only speech perception. On a behavioural level, while congruent mouth movement shortened the ESs’ response time for speech perception, the opposite effect was observed in JSs. Eye-tracking data revealed a gaze bias to the mouth for the ESs but not the JSs, especially before the audio onset. Additionally, the ERP P2 amplitude indicated that ESs processed multisensory speech more efficiently than auditory-only speech; however, the JSs exhibited the opposite pattern. Taken together, the ESs’ early visual attention to the mouth was likely to promote phonetic anticipation, which was not the case for the JSs. These results clearly indicate the impact of language and/or culture on multisensory speech processing, suggesting that linguistic/cultural experiences lead to the development of unique neural systems for audiovisual speech perception.

Impact of language on functional connectivity for audiovisual speech integration

Visual information about lip and facial movements plays a role in audiovisual (AV) speech perception. Although this has been widely confirmed, previous behavioural studies have shown interlanguage differences, that is, native Japanese speakers do not integrate auditory and visual speech as closely as native English speakers. To elucidate the neural basis of such interlanguage differences, 22 native English speakers and 24 native Japanese speakers were examined in behavioural or functional Magnetic Resonance Imaging (fMRI) experiments while mono-syllabic speech was presented under AV, auditory-only, or visual-only conditions for speech identification. Behavioural results indicated that the English speakers identified visual speech more quickly than the Japanese speakers, and that the temporal facilitation effect of congruent visual speech was significant in the English speakers but not in the Japanese speakers. Using fMRI data, we examined the functional connectivity among brain regions important for auditory-visual interplay. The results indicated that the English speakers had significantly stronger connectivity between the visual motion area MT and the Heschl’s gyrus compared with the Japanese speakers, which may subserve lower-level visual influences on speech perception in English speakers in a multisensory environment. These results suggested that linguistic experience strongly affects neural connectivity involved in AV speech integration.