Harumitsu Murohashi

Involvement of memory-comparison-based change detection in visual distraction

The involvement of memory-comparison-based change detection in visual distraction was elucidated. Not only luminance increments that engaged memory-comparison-based change detection and refractoriness-based rareness detection but also luminance decrements that engaged only memory-comparison-based change detection caused behavioral distraction, which was mirrored by a posterior negativity (240-260 ms, posterior N2) and a broad positivity (420-460 ms, P3a) that reflected attentional capture. Preceding these effects, luminance increments elicited a posterior positivity (100-120 ms, change-related positivity) and a posterior negativity (120-140 ms, change-related negativity), whereas luminance decrements elicited only a posterior positivity (160-180 ms, change-related positivity). These results suggest that memory-comparison-based change detection indexed by change-related positivity is involved in visual distraction as a result of attentional capture.

Neural correlates of preattentive and attentive processing of visual changes

To identify electrophysiological correlates of preattentive and attentive processing of visual changes, we compared event-related brain potentials in response to color changes at attended and unattended spatial locations using a visual S1–S2 matching task. The results showed that compared to no change, change stimuli elicited occipito-temporal positivity at around 100–160 ms (change-related positivity) and subsequent central negativity at around 220–300 ms (N270). Change-related positivity was observed in response to changes at both attended and unattended locations, while N270 was observed only when attention was directed to the location of the changes. These results suggest that change-related positivity reflects the preattentive processing of visual changes and N270 reflects the attentive processing of visual changes in the human brain.

Comprehension of degraded speech sounds with m-sequence modulation: an fMRI study.

In a recent electroencephalography (EEG) study (Takeichi et al., 2007a), we developed a new technique for assessing speech comprehension using speech degraded by m-sequence modulation and found a correlation peak with a 400-ms delay. This peak depended on the comprehensibility of the modulated speech sounds. Here we report the results of a functional magnetic resonance imaging (fMRI) experiment comparable to our previous EEG experiment. We examined brain areas related to verbal comprehension of the modulated speech sound to examine which neural system processes this modulated speech. A non-integer, alternating-block factorial design was used with 23 Japanese-speaking participants, with time reversal and m-sequence modulation as factors. A main effect of time reversal was found in the left temporal cortex along the superior temporal sulcus (BA21 and BA39), left precentral gyrus (BA6) and right inferior temporal gyrus (BA21). A main effect of modulation was found in the left postcentral gyrus (BA43) and the right medial frontal gyri (BA6) as an increase by modulation and in the left temporal cortex (BA21, 39), parahippocampal gyrus (BA34), posterior cingulate (BA23), caudate and thalamus and right superior temporal gyrus (BA38) as a decrease by modulation. An interaction effect associated specifically with non-modulated speech was found in the left frontal gyrus (BA47), left occipital cortex in the cuneus (BA18), left precuneus (BA7, 31), right precuneus (BA31) and right thalamus (forward>reverse). The other interaction effect associated specifically with modulation of speech sound was found in the inferior frontal gyrus in the opercular area (BA44) (forward>reverse). Estimated scalp projection of the component correlation function (Cao et al., 2002) for the corresponding EEG data (Takeichi et al., 2007a, showed leftward dominance. Hence, activities in the superior temporal sulcus (BA21 and BA39), which are commonly observed for speech processing, as well as left precentral gyrus (BA6) and left inferior frontal gyrus in the opercular area (BA44) is suggested to contribute to the comprehension-related EEG signal.

Underlying mechanisms of the P3a task-difficulty effect.

In three-stimulus oddball studies, even typical deviant stimuli elicited a large P3a event-related brain potential (ERP) when target/standard discrimination was difficult. To investigate the underlying mechanisms, the effects of task difficulty on early deviant-related ERPs were assessed. Four visual stimuli defined by an orthogonal combination of task-relevant size (nontarget 80%, target 20%) and task-irrelevant luminance (standard 80%, deviant 20%) were presented randomly, where two task difficulties (easy, difficult) were defined by target/nontarget discriminability. An increase in task difficulty enhanced P3a as well as a posterior negativity (change-related negativity) and an anterior positivity (frontal positivity) elicited by deviant nontarget stimuli. These results suggest that attentional modulation of refractoriness-based rareness detection and an attention-triggering process underlie the P3a task-difficulty effect.

Individuals with Asperger's disorder exhibit difficulty in switching attention from a local level to a global level.

The purpose of the present study was to determine whether individuals with Asperger’s disorder exhibit difficulty in switching attention from a local level to a global level. Eleven participants with Asperger’s disorder and 11 age- and gender-matched healthy controls performed a level-repetition switching task using Navon-type hierarchical stimuli. In both groups, level-repetition was beneficial at both levels. Furthermore, individuals with Asperger’s disorder exhibited difficulty in switching attention from a local level to a global level compared to control individuals. These findings suggested that there is a problem with the inhibitory mechanism that influences the output of enhanced local visual processing in Asperger’s disorder.

Working memory capacity affects the interference control of distractors at auditory gating

It is important to understand the role of individual differences in working memory capacity (WMC). We investigated the relation between differences in WMC and N1 in event-related brain potentials as a measure of early selective attention for an auditory distractor in three-stimulus oddball tasks that required minimum memory. A high-WMC group (n=13) showed a smaller N1 in response to a distractor and target than did a low-WMC group (n=13) in the novel condition with high distraction. However, in the simple condition with low distraction, there was no difference in N1 between the groups. For all participants (n=52), the correlation between the scores for WMC and N1 peak amplitude was strong for distractors in the novel condition, whereas there was no relation in the simple condition. These results suggest that WMC can predict the interference control for a salient distractor at auditory gating even during a selective attention task.

Effects of feature and spatial attention on visual change detection.

In event-related brain potential studies using a visual S1–S2 matching task, stimulus changes elicit change-related positivity, which reflects the detection of visual changes. To investigate the effects of attention on change detection, we tested the elicitation of change-related positivity in response to changes in color and spatial frequency under three attention conditions: (i) changes in an unattended feature at an attended location, (ii) in an attended feature at an unattended location, and (iii) in an unattended feature at an unattended location. The results suggest that stimulus changes can be detected even when both feature and spatial attention are withdrawn, but change detection can also be inhibited, which might be because of biased-competition determined by the combination of feature and spatial attention conditions.

Attention that covers letters is necessary for the left-lateralization of an early print-tuned ERP in Japanese hiragana

Extensive experience with reading develops expertise in acquiring information from print, and this is reflected in specific enhancement of the left-lateralized N170 component in event-related potentials. The N170 is generally considered to reflect visual/orthographic processing; while modulations of its left-lateralization related to phonological processes have also been indicated. However, in our previous study, N170-like response to Hiragana strings lacked left-lateralization when the stimuli were completely task-irrelevant in rapid-presentation sequences [Okumura et al. (2014). Early print-tuned ERP response with minimal involvement of linguistic processing in Japanese Hiragana strings. Neuroreport 25, 410-414]. This suggests that, despite the highly transparent character-to-syllable correspondence, the phonological mapping of Hiragana strings requires some kind of attention toward print. To verify this notion, the present study examined ERPs under the same experimental condition as in the previous study, except that the task required attention to a stimulus attribute (i.e., color). As a result, Hiragana words and nonwords elicited left-lateralized negative deflection in the occipito-temporal region during 130-170ms post-stimulus in comparison to symbol strings, but only when the print had a narrow intercharacter spacing. Moreover, we observed the enhancement of very early occipital ERP in response to words during 70-100ms. The present results suggest that visual attention plays a role in early print processing, which may contribute to our understanding of the mechanisms that underlie expert as well as impaired reading.

Early print-tuned ERP response with minimal involvement of linguistic processing in Japanese Hiragana strings.

The act of reading leads to the development of specific neural responses for print, the most frequently reported of which is the left occipitotemporal N170 component of event-related potentials. However, it remains unclear whether this electrophysiological response solely involves print-tuned neural activities. The present study examined an early print-tuned event-related potential response with minimal involvement of linguistic processing in a nonalphabetic language. Japanese Hiragana words, nonwords, and alphanumeric symbol strings were presented rapidly and the task was to detect the change in color of a fixation cross to restrict linguistic processing. As a result, Hiragana words and nonwords elicited a larger posterior N1 than alphanumeric symbol strings bilaterally, irrespective of intercharacter spacing. The fact that this N1 was enhanced specifically for rapidly presented Hiragana strings suggests the existence of print-tuned neural processes that are relatively independent of the influence of linguistic processing.

Role of the prefrontal cortex in the cognitive control of reaching movements: near-infrared spectroscopy study

To elucidate the role of the prefrontal cortex in cognitive control of reaching movements, by multichannel near-infrared spectroscopy we examine changes in oxygenated hemoglobin (oxy-Hb) as an indicator of changes in regional cerebral blood flow in the bilateral dorsolateral (DLPFC), ventrolateral prefrontal cortex (VLPFC), and frontopolar cortex (FPC) during a reaching task with normal visual feedback (a consistent task) and a reaching task with flipped horizontal visual feedback (an inconsistent task). Subjects first perform 12 trials of the consistent task, and then perform six blocks of the inconsistent task, each of which consists of six trials. During the consistent task, oxy-Hb is increased only in the right VLPFC. During the first block of the inconsistent task, increases in oxy-Hb are observed in the bilateral DLPFC and the right VLPFC, whereas the increased oxy-Hb was gradually reduced as the block proceeded, which was accompanied by an improvement in the task performance. Eventually, there were no differences in the degree of change in oxy-Hb between the consistent and inconsistent tasks in the DLPFC and VLPFC. These findings suggest that the DLPFC is engaged in higher order cognitive control, while the right VLPFC is engaged in both higher and lower order cognitive controls.