Takatsune Kumada

The attentional blink is governed by a temporary loss of control

Identification of the second of two brief targets is impaired at intertarget lags of less than about 500 msec. We compared two accounts of thisattentional blink (AB) by manipulating the number of digit distractors—and hence the lag—inserted among three letter targets in a rapid serial visual presentation stream of digit distractors. On the resource-depletion hypothesis, longer lags provide more time for processing the leading target, thus releasing resources for the trailing target. On the temporary-loss-of-control (TLC) hypothesis, intervening distractors disrupt the current attentional set, producing a trailing-target deficit. Identification accuracy for trailing targets was unimpaired not only at lag 1 (conventional lag 1 sparing) but also at later lags, if preceded by another target. The results supported the TLC hypothesis but not the resource-depletion hypothesis. We conclude that the AB is caused by a disruption in attentional set when a distractor is presented while the central executive is busy processing a leading target.

Feature-based control of attention: evidence for two forms of dimension weighting.

In three experiments, I examined whether prior knowledge of a target feature dimension is useful for guiding spatial attention to the target in a variety of tasks: visual search (Experiments 1A and 1B), texture segregation (Experiment 2), and visual enumeration (Experiment 3). Experiment 1A used a simple search task and found that reaction times for blocks in which a target was defined within a single feature dimension were shorter than those for blocks in which a target was defined across dimensions (within-dimension facilitation; WDF). Intertrial facilitation (ITF; Müller, Heller, & Ziegler, 1995), a dimension-based priming effect from one trial to the immediately following one, was also observed. Both WDF and ITF disappeared when the same stimuli were used under a compound search task (Experiment 1B), in which participants responded to an attribute of the target in a feature dimension different from its defining dimensions. Experiments 2 and 3 showed that WDF and ITF are not necessarily contingent upon each other: In a texture discrimination task, only WDF was found; in an enumeration task for six or seven targets, only ITF was found. These results show that the two forms of dimension weighting, WDF and ITF, are mediated by different mechanisms. WDF was eliminated when focal attention to targets was required, suggesting that feature-based modulation is limited as a source for controlling spatial attention (Kumada, 1999). ITF was correlated with type of response, suggesting dimension-specific response mechanisms (Cohen & Shoup, 1997).

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.

Lexical recovery from extinction: Interactions between visual form and stored knowledge modulate visual selection.

The effects of lexical knowledge on extinction were examined in a patient with bilateral parietal lesions and left extinction under double simultaneous stimulation: GK. GK was bilaterally presented with two letters that could form either a word or a nonword. In Experiments 1–3, the task was to identify each letter. GK showed better identification of left-side letters in words than in nonwords, whilst the identification of left-side letters in nonwords was worse than that of single letters presented in the same spatial positions (i.e., there was a word superiority effect under conditions in which extinction occurred). This lexical effect on completely correct responses tended to be larger for words with lower-case letters (Experiments 2 and 3) than for words with upper-case letters (Experiment 1). Different results arose when detection was measured. When letters could group by proximity and common contrast polarity, no word superiority effect was apparent. However, a word superiority effect re-emerged when low-level grouping was reduced by using letters with opposite contrast polarity (one white and one black on a grey background). The results are discussed in terms of the impact of different factors on selection in detection and identification tasks, and in terms of the modulatory roles of familiar form and stored knowledge on visual selection.

Limitations in attending to a feature value for overriding stimulus-driven interference.

Six experiments were conducted to examine the effect of knowledge of a target for overriding stimulus-driven interference in simple search tasks (Experiments 1–3) and compound search tasks (Experiments 4–6). In simple search when the target differed from nontargets in orientation, a singleton distractor that had an orientation equivalent to that of a target interfered with search for the target. When the singleton distractor was less salient than the target with respect to the target-defining feature, it still caused interference. Such within-dimensional, nonsaliency-based interference also occurred in compound search tasks. In contrast, no interference occurred when a singleton distractor was defined in cross-dimension in a simple search task. When a compound search task was used, the salient distractor interfered with the search for a less salient target. These results are discussed in terms of their applicability to existing models and the limitations of top-down penetrability of a feature processing stage.

Cross-dimensional interference and cross-trial inhibition.

In two experiments, we examined whether one source of cross-dimensional interference in visual search involves cross-trial position priming. In Experiment 1, we demonstrated cross-dimensional interference in search for an orientation-defined target: Search for a left-tilted target among right-tilted nontargets was disrupted by the presence of a singleton color distractor. In all conditions, search was facilitated when a target was presented at the same position as a target in the previous trial (positive position priming). In addition, there were negative effects of position priming on orientation targets that fell on the same side as singleton distractors on the previous trial. In Experiment 2, to examine the impact of negative position priming on cross-dimensional interference, trials with and without singleton distractors were presented in a single trial block. The chance of a singleton distractor’s being present on a preceding trial was then equated across displays when the distractor was and when it was not subsequently present. Cross-dimensional interference was eliminated under this mixed presentation condition, suggesting that the cost of cross-dimensional interference was not determined by the stimulus-driven factors in the current trial, at least when a limited number of target and distractor locations was used. We conclude that top-down selection is possible during visual search, and this leads to inhibition of the location of salient distractors. The cost of this is slowed detection of targets at inhibited locations on subsequent trials.

Attending to a location in three-dimensional space modulates early ERPs

It has been reported that attending to a particular location can modulate incoming sensory signals, as reflected by the stimulus-evoked P1 and N1 components of the visual event-related potential (ERPs) in a two-dimensional (2D) display [Attention, Space, and Action: Studies in Cognitive Neuroscience, Oxford University Press, New York, 1999, p. 31]. In contrast, in this study we examined the effect of attention in 3D space using a stereoscopic display. Stimuli were presented randomly, one at a time, in an orthogonal combination of two depths (near, far) and two 2D locations (left, right) relative to the fixation point. The task was to attend selectively to one of these four positions and to respond to a target stimulus defined by shape in the attended 3D location. The effect of 2D location selection on the P1 amplitude was greater for stimuli in the near than the far depth plane, and the amplitude of N1 increased in response to stimuli in the attended combination of 2D location and depth. These results suggest that the effect of early spatial selection on the visual ERP is not simply based on retinotopic organization of the visual field, but also on intermediate stages that construct a 3D spatial representation of the external world.

Probing attentional modulation of contextual cueing

The repetition of spatial layout implicitly facilitates visual search (contextual cueing effect; Chun & Jiang, 1998). Although a substantial number of studies have explored the mechanism underlying the contextual cueing effect, the manner in which contextual information guides spatial attention to a target location during a visual search remains unclear. We investigated the nature of attentional modulation by contextual cueing, using a hybrid paradigm of a visual search task and a probe dot detection task. In the case of a repeated spatial layout, detection of a probe dot was facilitated at a search target location and was inhibited at distractor locations relative to nonrepeated spatial layouts. Furthermore, these facilitatory and inhibitory effects possessed different learning properties across epochs (Experiment 1) and different time courses within a trial (Experiment 2). These results suggest that contextual cueing modulates attentional processing via both facilitation to the location of “to-be-attended” stimuli and inhibition to the locations of “to-be-ignored” stimuli.

The spatial distribution of inhibition in preview search.

In an inefficient visual search task, when some distractors (old items) temporally precede some others (new items), the old items are excluded from the search, a phenomenon termed visual marking. This effect is said to occur because the locations of the old items are inhibited before the new items appear. The present study used a probe-detection task to examine whether this inhibition occurs only at the precise locations of old items or at and around the locations of old items. We also investigated the effect of inhibition overreaching boundaries to encompass neighboring regions. Participants searched for a target or detected a probe that appeared after the new items appeared. The results revealed that the probe reaction times at locations inside grouped regions were longer than those at a blank region where no items had been presented and were comparable to those at a location occupied by old items. Probe detection was not delayed when the probe was presented near but external to the external boundary of the grouped regions. The overreaching effect was obtained before and after the new items appeared. We conclude that the inhibitory template for visual marking represents clusters of old items for at least 200 ms before the onset of new items, and that this spatial schema is preserved until at least 200 ms after the onset of new items.

The encoding process of nonconfigural information in contextual cuing

National Institute of Advanced Industrial Science and Technology, Ibaraki, Japan Jiang and Wagner (2004) demonstrated that individual target—distractor associations were learned in contextual cuing. We examined whether individual associations can be learned in efficient visual searches that do not involve attentional deployment to individual search items. In Experiment 1, individual associations were not learned during the efficient search tasks. However, in Experiment 2, where additional exposure duration of the search display was provided by presenting placeholders marking future locations of the search items, individual associations were successfully learned in the efficient search tasks and transferred to inefficient search. Moreover, Experiment 3 demonstrated that a concurrent task requiring attention does not affect the learning of the local visual context. These results clearly showed that attentional deployment is not necessary for learning individual locations and clarified how the human visual system extracts and preserves regularity in complex visual environments for efficient visual information processing.