Eriko Matsumoto

Neural mechanisms of spatial stimulus-response compatibility: the effect of crossed-hand position.

Previous psychological experiments have indicated the existence of a visual–proprioceptive interaction in spatial stimulus–response compatibility (SSRC) tasks, but there is little specific information on the neural basis of such interaction in humans. Using functional magnetic resonance imaging (fMRI), we compared the neural activity associated with two different aspects of spatial coding: the coding of the “internal” spatial position of motor-response effectors (i.e., the position of body parts) as obtained through proprioception, and the coding of “external” positions, i.e., the positions of visual stimuli. A 2×2 factorial design was used to investigate the spatial compatibility (incompatible versus compatible) between a visual stimulus and hand position (crossed versus uncrossed). The subjects were instructed to respond to stimuli presented to the right or left visual field with either the ipsilateral (compatible condition) or the contralateral hand (incompatible condition). The incompatible condition produced stronger activation in the bilateral superior parietal lobule, inferior parietal lobule, and bilateral superior frontal gyrus than the compatible condition. The crossed-hand condition produced stronger activation in the bilateral precentral gyrus, superior frontal gyrus, superior parietal lobule, and superior temporal gyrus than the uncrossed-hand condition. These results suggest that activity in the frontal–parietal regions is related to two functions: (1) representation of the visual stimulus–motor response spatial configuration in an SSRC task, and (2) integration between external visual and internal proprioceptive sensory information. The activation in the superior temporal gyrus was not affected by the visual stimulus–motor response spatial configuration in an SSRC task; rather, it was affected by the crossed-hand posture. Thus, it seems to be related to representing internal proprioceptive sensory information necessary to carry out motor actions.

Phonological influences on lexicosemantic processing of kanji words.

To investigate the phonological influences on the lexicosemantic process with a strong orthographic constraint, we used kanji (morphogram) homophone words and measured, using magnetoencephalography, the neural activities during the silent reading of prime-target pairs. The primes were phonologically the same as or different from the targets or pseudocharacters. The neural activities in the left posterior temporal and inferior parietal areas became weaker with phonological repetition. Furthermore, stronger activities for the different condition in the left anterior temporal area and for the same condition in the left inferior frontal cortex, respectively, suggest the roles of these areas of the brain in the semantic processing of words and in the selection of appropriate meanings. We conclude that phonological information affects the lexicosemantic process even with a strong orthographic constraint.

Numerosity underestimation in sets with illusory contours

People underestimate the numerosity of collections in which a few dots are connected in pairs by task-irrelevant lines. Such configural processing suggests that visual numerosity depends on the perceived scene segments, rather than on the perceived total area occupied by a collection. However, a methodology that uses irrelevant line connections may also introduce unnecessary distraction and variety, or obscure the perception of task-relevant items, given the saliency of the lines. To avoid such potentially confounding variables, we conducted four experiments where the line-connected dots were replaced with collinear inducers of Kanizsa-type illusory contours. Our participants had to compare two simultaneously presented collections and choose the more numerous one. Displays comprised c-shaped inducers and disks (Experiment 1), c-shaped inducers only (Experiments 2 and 4), or closed inducers (Experiment 3). One display always showed a 12- (Experiments 1-3) or 48-item reference pattern (Experiment 4); the other was a test pattern with numerosity varying between 9 and 15 (Experiments 1-3) or 36-60 items (Experiment 4). By manipulating the number of illusory contours in the test patterns, the level of connectedness increased or decreased respectively. The fitted psychometric functions revealed an underestimation that increased with the number of illusory contours in Experiments 1 and 2, but was absent in Experiments 3 and 4, where illusory contours were more difficult to perceive or larger numerosities were used. Results corroborate claims that visual numerosity estimation depends on segmented inputs, but only within moderate numerical ranges.

Cognitive Control of Attentional Guidance by Visual and Verbal Working Memory Representations

Both visual and verbal information in working memory guide visual attention toward a memory-matching object. We tested whether: (a) visual and verbal representations have different effects on the deployment of attention; and (b) both types of representations can be used equally in a top-down manner. We asked participants to maintain a visual cue or a verbal cue at the beginning of each trial, and ended with a memory task to ensure that each cue was represented actively in working memory. Before the memory task, a visual search task appeared where validity was manipulated as valid, neutral, or invalid. We also manipulated the probability of valid trials (20%, 50%, and 80%), which had been told to the participants prior to the task. Consistent with earlier findings, attentional guidance by visual representations was modulated by the probability. We also found that this was true for verbal representations, and that these effects did not differ between representation types. These results suggest that both visual and verbal representations in working memory can be used strategically to control attentional guidance.

Relative spatial frequency tuning and its contrast dependency in human perception

Several physiological studies in cats and monkeys have reported that the spatial frequency (SF) tuning of visual neurons varies depending on the luminance contrast and size of stimulus. However, comparatively little is known about the effect of changing the stimulus contrast and size on SF tuning in human perception. In the present study, we investigated the effects of stimulus size and luminance contrast on human SF tuning using the subspace-reverse-correlation method. Measuring SF tunings at six different stimulus sizes and three different luminance contrast conditions (90%, 10%, and 1%), we found that human perception exhibits significant stimulus-size-dependent SF tunings. At 90% and 10% contrast, participants exhibited relative SF tuning (cycles/image) rather than absolute SF tuning (cycles/°) at response peak latency. On the other hand, at 1% contrast, the magnitude of the size-dependent-peak SF shift was too small for strictly relative SF tuning. These results show that human SF tuning is not fixed, but varies depending on the stimulus size and contrast. This dependency may contribute to size-invariant object recognition within an appropriate contrast rage.

Asymmetric activation to the context-dependent right in the right inferior frontal region

In human spatial recognition, right and left are not recognized symmetrically. Although there have been many studies on the hemispheric asymmetry of the human brain, asymmetries in high‐level recognition (such as independence from input or output hemisphere) have not been studied extensively. We found that the human brain recognizes right and left asymmetrically in high‐level recognition. Experiments were performed in which participants crossed their hands and were required to judge the side of a tactile stimulus on the index finger in two different contexts: ‘which hand was touched’ or ‘on which side of the space the touched hand was located’. The right inferior frontal region was significantly more activated by the ‘contextually defined right’ stimulus (right‐hand stimulation in the ‘which hand’ context and right‐space stimulation in the ‘which space’ context) than by the ‘contextually defined left’ stimulus. However, no activation that was more activated by the ‘contextually defined left’ than by the ‘contextually defined right’ was found. This asymmetric activation suggests that ‘right’ is the more outstanding side for human spatial recognition.

Negative cues lead to more inefficient search than positive cues even at later stages of visual search

Observers can focus their attention on task-relevant items in visual search when they have prior knowledge about the targets properties (i.e., positive cues). However, little is known about how negative cues, which specify the features of task-irrelevant items, can be used to guide attention away from distractors and how their effects differ from those of positive cues. It has been proposed that when a distractor color is cued, people would first select the to-be-ignored items early in search and then inhibit them later. The present study investigated how the effects of positive and negative cues differ throughout the visual search process. The results showed that positive cues sped up the early stage of visual search and that negative cues led to initial selection for inhibition. We further found that visual search with negative cues was more inefficient than that with positive cues even at later stages, suggesting that sustained inhibition is needed throughout the visual search process. Taken together, the results indicate that positive and negative cues have different functions: prior knowledge about target features can weight task-relevant information at early stages of visual search, and negative cues are used more inefficiently even at later stages of visual search.

Electrophysiological evidence that top-down knowledge controls working memory processing for subsequent visual search.

Items in working memory guide visual attention toward a memory-matching object. Recent studies have shown that when searching for an object this attentional guidance can be modulated by knowing the probability that the target will match an item in working memory. Here, we recorded the P3 and contralateral delay activity to investigate how top–down knowledge controls the processing of working memory items. Participants performed memory task (recognition only) and memory-or-search task (recognition or visual search) in which they were asked to maintain two colored oriented bars in working memory. For visual search, we manipulated the probability that target had the same color as memorized items (0, 50, or 100%). Participants knew the probabilities before the task. Target detection in 100% match condition was faster than that in 50% match condition, indicating that participants used their knowledge of the probabilities. We found that the P3 amplitude in 100% condition was larger than in other conditions and that contralateral delay activity amplitude did not vary across conditions. These results suggest that more attention was allocated to the memory items when observers knew in advance that their color would likely match a target. This led to better search performance despite using qualitatively equal working memory representations.

Is visual working memory modulated by prior knowledge about probability? An ERP study

Prominent theories of visual attention claim that the contents of visual working memory (VWM) can guide attention during visual search. This is supported by numerous experimental observations showing that information held in VWM automatically captures attention (e.g., Soto et al., 2008, Trends Cong Sci). Recently, Carlisle & Woodman (2011, Acta Psychol) reported that the effects of attentional capture varied according to prior instructions about the probability of memory-match trials, which suggests that strategic use of the contents held in VWM may alter visual search performance. However, it remains unclear how these instructions influence the contents stored in VWM. In the present study, we used contralateral delay activity (CDA) as an electrophysiological index of VWM load. The task was to conduct visual search while holding an item in VWM. There were three within-subjects conditions, across which we pre-informed participants about the probability (20%, 50%, or 80%) of memory-match trials. We hypothesized that VWM would be more loaded with more probability of memory-match trials. We found that RT costs (invalid minus neutral trials) in the 80% condition were larger than in the 20% and 50% conditions, but there were no between-condition differences in RT benefits (valid minus neutral trials). These results indicate that prior knowledge about probability affected RT costs only. Unexpectedly, CDA was only obtained in 50% condition. These results imply that knowledge about biased-probability (20% and 80%) leads to a decrease in the demands to attend to or hold to-be-memorized item. In conclusion, the present ERPs findings, combined with the RT results, suggest that changes in RT costs across conditions by instruction may not depend on VWM activity as measured by CDA. Meeting abstract presented at VSS 2015.