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Masato Taira

Publications and source records attributed to Masato Taira.

23 records · Page 2Linked to original sources
PubMed2004

Reading in a regular orthography: an FMRI study investigating the role of visual familiarity.

In order to separate the cognitive processes associated with phonological encoding and the use of a visual word form lexicon in reading, it is desirable to compare the processing of words presented in a visually familiar form with words in a visually unfamiliar form. Japanese Kana orthography offers this possibility. Two phonologically equivalent but visually dissimilar syllabaries allow the writing of, for example, foreign loanwords in two ways, only one of which is visually familiar. Familiarly written words, unfamiliarly written words, and pseudowords were presented in both Kana syllabaries (yielding six conditions in total) to participants during an fMRI measurement with a silent articulation task (Experiment 1) and a phonological lexical decision task (Experiment 2) using an event-related design. Consistent over two experimental tasks, the three different stimulus types (familiar, unfamiliar, and pseudoword) were found to activate selectively different brain regions previously associated with phonological encoding and word retrieval or meaning. Compatible with the predictions of the dual-route model for reading, pseudowords and visually unfamiliar words, which have to be read using phonological assembly, caused an increase in brain activity in left inferior frontal regions (BA 44/47), as compared to visually familiar words. Visually familiar and unfamiliar words were found to activate a range of areas associated with lexico-semantic processing more strongly than pseudowords, such as the left and right temporo-parietal region (BA 39/40), a region in the left middle/inferior temporal gyrus (BA 20/21), and the posterior cingulate (BA 31).

Adolescent↗
PubMed2003

Short-term memory and perceptual decision for three-dimensional visual features in the caudal intraparietal sulcus (Area CIP).

The purpose of the present study was to examine whether neurons in the caudolateral part of the intraparietal sulcus (area CIP), a part of the posterior parietal cortex, contribute to short-term memory and perceptual decision of three-dimensional (3D) surface orientation, in addition to its purely visual nature of responding selectively to 3D surface orientation. Activities of CIP neurons were recorded while monkeys performed a modified delayed matching-to-sample (DMTS) task using stereoscopic stimuli. Seventy-seven neurons were examined with a routine of the DMTS task, and 94% (72 of 77) of them showed selectivity to surface orientation. Furthermore, 82% (63 of 77) of the examined neurons showed sustained activity during delay, and 60% (38 of 63) of them showed selective delay activity depending on the sample stimulus, suggesting that they contribute to short-term memory of 3D visual features. On the other hand, 53% (41 of 77) of the examined neurons showed modulation of visual response depending on whether a stimulus appeared as a sample, match, or nonmatch stimulus (contextual modulation). The majority (73%, 30 of 41) of these neurons with contextual modulation showed activity change depending on whether the test stimuli did or did not match the sample stimuli (match-nonmatch modulation), suggesting their involvement in matching, or perceptual decision, concerning 3D visual features. These findings suggest that CIP neurons play important roles not only in the perception of 3D visual features but also in cognitive functions such as short-term memory and perceptual decision of 3D visual information.

Animals↗
PubMed2002

Selective attention regulates spatial and intensity information processing in the human primary somatosensory cortex.

Attention-related cognitive processes in the primary somatosensory cortex (SI) were studied by measuring somatosensory evoked magnetic fields (SEFs). Twenty-one normal adult human subjects participated in this study for investigating effects of attention and stimulus intensity on cortical finger representation in the SI cortex. Electric stimuli at low and high intensity were delivered to the index or middle finger in finger discrimination and non-discrimination task. For the low intensity stimulation at 1.25 times sensory threshold, an early component (M50) showed clear segregation of the sources for the two fingers and an increase of the amplitude specific to the finger discrimination task. Such an attentional effect on the SI cortex was masked by the high intensity stimulation (2.5 times sensory threshold); the M50 source separation by the fingers was induced irrespective of the discrimination or non-discrimination task. The results suggest that a conscious regulation of stimulus intensity coding in the SI cortex underlies the attention-dependent enhancement of spatial finger information processing.

Adult↗
PubMed2002

Neural correlates for perception of 3D surface orientation from texture gradient.

A goal in visual neuroscience is to reveal how the visual system reconstructs the three-dimensional (3D) representation of the world from two-dimensional retinal images. Although the importance of texture gradient cues in the process of 3D vision has been pointed out, most studies concentrate on the neural process based on binocular disparity. We report the neural correlates of depth perception from texture gradient in the cortex. In the caudal part of the lateral bank of intraparietal sulcus, many neurons were selective to 3D surface orientation defined by texture gradient, and their response was invariant over different types of texture pattern. Most of these neurons were also sensitive to a disparity gradient, suggesting that they integrate texture and disparity gradient signals to construct a generalized representation of 3D surface orientation.

Animals↗