Kazuhiko Yokosawa

Visual search and memory search engage extensive overlapping cerebral cortices: an fMRI study

Previous studies have investigated neural correlates of visual search and memory search independently, but none of those studies examined whether cortical regions involved in these searches are overlapping or segregated by directly comparing the two types of search. In this study, we compared the cortical regions involved in visual search and memory search in the same functional magnetic resonance imaging (fMRI) experiment run on the same subjects, using identical stimuli and time courses of stimulus presentation. The right dorsolateral prefrontal cortex (DLPFC), the left frontal eye field (FEF), the right precuneus and cuneus, and the left cerebellum were activated by both visual search and memory search. We suggest that the right DLPFC is associated with the process of monitoring and manipulating multiple elements, while the left FEF is involved in cognitive planning. We also propose that the right precuneus and cuneus as well as the left cerebellum are responsible for both spatial and nonspatial shifts of attention, including attentional shifts in long-term memory, although each of these regions has a slightly different role.

Synesthetic colors for Japanese late acquired graphemes

Determinants of synesthetic color choice for the Japanese logographic script, Kanji, were studied. The study investigated how synesthetic colors for Kanji characters, which are usually acquired later in life than other types of graphemes in Japanese language (phonetic characters called Hiragana and Katakana, and Arabic digits), are influenced by linguistic properties such as phonology, orthography, and meaning. Of central interest was a hypothesized generalization process from synesthetic colors for graphemes, learned prior to acquisition of Kanji, to Kanji characters learned later. Results revealed that color choices for Kanji characters depend on meaning and phonological information. Some results suggested that colors are generalized from Hiragana characters and Arabic digits to Kanji characters via phonology and meaning, respectively. Little influence of orthographic information was observed. The findings and approach of this study contributes to a clarification of the mechanism underlying grapheme-color synesthesia, especially in terms of its relationship to normal language processing.

Synesthetic colors are elicited by sound quality in Japanese synesthetes.

Determinants of synesthetic color choice for Japanese phonetic characters were studied in six Japanese synesthetes. The study used Hiragana and Katakana characters, which represent the same set of syllables although their visual forms are dissimilar. From a palette of 138 colors, synesthetes selected a color corresponding to each character. Results revealed that synesthetic color choices for Hiragana characters and those for their Katakana counterparts were remarkably consistent, indicating that color selection depended on character-related sounds and not visual form. This Hiragana-Katakana invariance cannot be regarded as the same phenomenon as letter case invariance, usually reported for English grapheme-color synesthesia, because Hiragana and Katakana characters have different identities whereas upper and lower case letters have the same identity. This involvement of phonology suggests that cross-activation between an inducer (i.e., letter/character) brain region and that of the concurrent (i.e., color) area in grapheme-color synesthesia is mediated by higher order cortical processing areas.

Effects of laterality and pitch height of an auditory accessory stimulus on horizontal response selection: the Simon effect and the SMARC effect.

In the present article, we investigated the effects of pitch height and the presented ear (laterality) of an auditory stimulus, irrelevant to the ongoing visual task, on horizontal response selection. Performance was better when the response and the stimulated ear spatially corresponded (Simon effect), and when the spatial—musical association of response codes (SMARC) correspondence was maintained—that is, right (left) response with a high-pitched (low-pitched) tone. These findings reveal an automatic activation of spatially and musically associated responses by task-irrelevant auditory accessory stimuli. Pitch height is strong enough to influence the horizontal responses despite modality differences with task target.

Illusory Line Motion in Visual Search: Attentional Facilitation or Apparent Motion?

A line, presented instantaneously, is perceived to be drawn from one end when a dot is flashed at that end prior to the presentation of the line. Although this phenomenon, called illusory line motion, has been attributed to accelerated processing at the locus of attention, preattentive (stimulus-driven) motion mechanisms might also contribute to the line-motion sensation. We tested this possibility in an odd-target-search task. The stimulus display consisted of two, four, or eight pairs of dots and lines. All lines were presented on the same side of the dots (eg right), except for the target line, which was presented on the opposite side (left). Subjects were asked to report the presence or absence of the target, which was presented in half of the trials. Low error rates for target detection (about 10%) even when the display consisted of eight dot-line pairs (ie display size was eight) indicated that illusory line motion could be perceived simultaneously at many locations. The interstimulus interval (ISI) between the dots and lines (0–2176 ms) and the contrast polarity (both dots and lines were brighter than the background, or dots were darker and lines were brighter) were also manipulated. When an ISI of a few hundred milliseconds was inserted, target detection was nearly impossible with larger display sizes. When the contrast polarity was changed, the target-detection performance was impaired significantly, even with no ISI. Moreover, it was found that the effects of display size, ISI, and contrast polarity were comparable in searches for a two-dot apparent-motion target. These results support the idea that preattentive, apparent-motion mechanisms, as well as attentional mechanisms, contribute to illusory line motion.

Orthogonal stimulus–response compatibility effects emerge even when the stimulus position is task irrelevant

The above-right/below-left mapping advantage with vertical stimuli and horizontal responses is known as the orthogonal stimulus–response compatibility (SRC) effect. We investigated whether the orthogonal SRC effect emerges with irrelevant stimulus dimensions. In Experiment 1, participants responded with a right or left key press to the colour of the stimulus presented above or below the fixation. We observed an above-right/below-left advantage (orthogonal Simon effect). In Experiment 2, we manipulated the polarity in the response dimension by varying the horizontal location of the response set. The orthogonal Simon effect decreased and even reversed as the left response code became more positive. This result provides evidence for the automatic activation of the positive and negative response codes by the corresponding positive and negative stimulus codes. These findings extended the orthogonal SRC effect based on coding asymmetry to an irrelevant stimulus dimension.

Grouping and Trajectory Storage in Multiple Object Tracking: Impairments Due to Common Item Motions

In our natural viewing, we notice that objects change their locations across space and time. However, there has been relatively little consideration of the role of motion information in the construction and maintenance of object representations. We investigated this question in the context of the multiple object tracking (MOT) paradigm, wherein observers must keep track of target objects as they move randomly amid featurally identical distractors. In three experiments, we observed impairments in tracking ability when the motions of the target and distractor items shared particular properties. Specifically, we observed impairments when the target and distractor items were in a chasing relationship or moved in a uniform direction. Surprisingly, tracking ability was impaired by these manipulations even when observers failed to notice them. Our results suggest that differentiable trajectory information is an important factor in successful performance of MOT tasks. More generally, these results suggest that various types of common motion can serve as cues to form more global object representations even in the absence of other grouping cues.

Grapheme learning and grapheme-color synesthesia: toward a comprehensive model of grapheme-color association

Recent progress in grapheme-color synesthesia research has revealed that certain regularities, as well as individual differences, figure into grapheme-color associations. Although several factors are known to regulate grapheme-color associations, the impact of factors, including their interrelationships, on synesthesia remains unclear. We investigated determinants of synesthetic color for graphemes (characters, letters) of Hiragana, a phonetic script in the Japanese language, and the English alphabet. Results revealed that grapheme ordinality was the strongest predictor of synesthetic colors for Hiragana characters, followed by character sound, and visual shape. Ordinality and visual shapes also significantly predicted synesthetic colors for English alphabet letters, however, sounds did not. The relative impact of grapheme properties on grapheme-color associations and the differences between these two writing systems are accounted for by considering the way graphemes are processed in the brain and introduced during an individuals development. A new model is proposed which takes into account the developmental process of grapheme learning. The model provides comprehensive explanation of synesthetic grapheme-color association determination processes, including the differences across writing systems.

Does disruption of a scene impair change detection

When we view a scene, we generally feel that we have a rich representation of that scene. Recent research has shown, however, that we are unable to detect relatively large changes in scenes, which suggests an inability to retain the visual details from one scene view to the next. In the present study, we investigated whether we can retain and make use of global and semantic information from a scene in order to efficiently detect changes from one scene to the next. Results indicated that change detection was practically independent of scene disruption with one exception. Better performance in the meaningful scenes was observed only in the whole-scene presentation condition where the participants knew that the stimulus was extracted from the meaningful scene.

Ecological Effects in Cross‐Cultural Differences Between U.S. and Japanese Color Preferences

We investigated cultural differences between U.S. and Japanese color preferences and the ecological factors that might influence them. Japanese and U.S. color preferences have both similarities (e.g., peaks around blue, troughs around dark-yellow, and preferences for saturated colors) and differences (Japanese participants like darker colors less than U.S. participants do). Complex gender differences were also evident that did not conform to previously reported effects. Palmer and Schlosss (2010) weighted affective valence estimate (WAVE) procedure was used to test the Ecological Valence Theorys (EVTs) prediction that within-culture WAVE-preference correlations should be higher than between-culture WAVE-preference correlations. The results supported several, but not all, predictions. In the second experiment, we tested color preferences of Japanese-U.S. multicultural participants who could read and speak both Japanese and English. Multicultural color preferences were intermediate between U.S. and Japanese preferences, consistent with the hypothesis that culturally specific personal experiences during ones lifetime influence color preferences.