Audiovisual semantic interference and attention: Evidence from the attentional blink paradigm

In the present study we investigate the role of attention in audiovisual semantic interference, by using an attentional blink paradigm. Participants were asked to make an unspeeded response to the identity of a visual target letter. This target letter was preceded at various SOAs by a synchronized audiovisual letter-pair, which was either congruent (e.g. hearing an “F” and viewing an “F”) or incongruent (e.g. hearing an “F” and viewing a “Z”). In Experiment 1, participants were asked to match the members of the audiovisual letter-pair. In Experiment 2, participants were asked to ignore the synchronized audiovisual letter-pairs altogether and only report the visual target. In Experiment 3, participants were asked to identify only one of the audiovisual letters (identify the auditory letter, and ignore the synchronized visual letter, or vice versa). An attentional blink was found in all three experiments indicating that the audiovisual letter-pairs were processed. However, a congruency effect on subsequent target detection was observed in Experiments 1 and 3, but not in Experiment 2. The results indicate that attention to the semantic contents of at least one modality is necessary to establish audiovisual semantic interference.     

The time course of attentional capture under dual-task conditions

Several recent studies have shown that attentional capture is not an automatic process. For example, abrupt peripheral onsets do not affect the processing of targets presented subsequently at that location when participants have to concurrently perform a perceptually demanding task elsewhere. This result leaves open the question of whether peripheral onsets lose their effectiveness in capturing attention or whether, instead, the performance of a perceptually demanding task entails a faster disengagement of attention from the cued location. Here, we measured exogenous spatial attentional-orienting effects either while participants performed a concurrent perceptually demanding central-monitoring task (a rapid serial visual presentation of letters for a to-be-detected digit target; Experiments 1 and 2) or in isolation (the baseline condition in Experiment 2). The results showed that peripheral onsets captured participants' attention at both the 80- and 190-ms stimulus onset asynchronies (SOAs) in the baseline condition. Crucially, however, during concurrent central monitoring, peripheral onsets were effective in capturing attention only at an 80-ms SOA, while the orienting effect disappeared as soon as a changing letter drew participants' attention back to the central stream (at an SOA of 190 ms). These findings demonstrate that task-irrelevant abrupt onsets cannot be entirely overridden by top-down attentional control, although attentional capture effects are dramatically reduced by an ongoing perceptually demanding task.     

Visual orienting with central and peripheral precues: Deconfounding the contributions of cue eccentricity,cue discrimination and spatial correspondence

Five experiments examined effects of spatial precues on visual attention. Precues consisted of letters (X, T, O) presented bilaterally at central and peripheral locations.In the spatial correspondence conditions targets tended (p= .8) to appear on the same side as one of the letters. In the spatial translation conditions the bilateral letters were identical; one letter (e.g., X) indicated that the target would probably (p= .8) appear on the left, and the other (e.g., T) indicated that the target would probably appear on the right. In the spatial correspondence conditions (Experiments 1, 3A, 4, and 5) response latencies were quicker on valid than invalid trials, even at very brief (0 ms, 33 ms, 66 ms, 100 ms) stimulus onset asynchronies (SOAs) between cue and target onset. Also,the dynamic pattern of cost and benefit resembled that seen in previous studies with unilateral peripheral precues. In the spatial translation conditions (Experiments 2 and 3B), a clear advantage for valid trials was only apparent at somewhat longer SOAs (150 ms, 300 ms, 500 ms). Results show that the need to discriminate between cue stimuli, and the visual eccentricity of cues, are not critical factors mediating attentional effects of spatial precues. However, the presence or absence of spatial correspondence between the location of a cue stimulus and the location of the target was critically important.     

Attentional selection during preparation of eye movements

Two experiments were conducted to examine the relationship between visual attention and saccade programming. Participants had to saccade to a letter string and detect a letter change presented briefly before the saccade onset. Hit probability (i.e., correct detection of a letter change in different positions) was taken as a measure of visual attention focus. The first experiment shows that hit probability depends on the actual landing position. These findings argue for a spatial coupling between saccade programming and the orienting of attention. Also, an unfamiliar letter cluster at the beginning captures attention and prevails over the influence of the saccade in preparation. Experiment 2, in which the letter change occurred at different times during the saccade latency, shows that attention shifts and focuses on the saccade target at the expense of the other parts of the stimulus when the motor program is ready to be executed. The theoretical implications of these results are discussed.     

Selective attention and interhemispheric response competition in the split-brain

The interfering effect of an unattended stimulus on processing of an attended item was studied in a single split-brain participant (LB) and in normal controls. Pairs of letters were presented to the left visual field (LVF), right visual field (RVF), or bilaterally. Participants attended to the rightmost letter while attempting to ignore the leftmost letter. Responses associated with the attended and to-be-ignored letters could be compatible or incompatible. Manual response latencies were generally slower on Response Incompatible compared to Response Compatible trials. Notably, LB displayed this effect on Bilateral trials, where target and distractor were presented to opposite visual fields. LB was unable to perform a same-different matching task with bilateral letter stimuli, but was able to name bilateral letters accurately. Hence, in the bilateral condition, the ability to cross-compare letters was dissociated from attentional interference and from letter naming. Implications of these findings are discussed.     

A central capacity sharing model of dual-task performance

The authors present the central capacity sharing (CCS) model and derive equations describing its behaviors to explain results from dual-task situations. The predictions of the CCS model are contrasted with those of the central bottleneck model. The CCS model predicts all of the hallmark effects of the psychological refractory period (PRP) pardigm: -1 slope of the PRP effect at short stimulus onset asynchronies (SOAs), underadditivity of precentral Task 2 manipulations, additivity of central or postcentral Task 2 manipulations with SOA, and carry forward to Task 2 of Task 1 precentral or central manipulations at short SOAs. The CCS model also predicts that Task 1 response times increase with decreasing SOA. The model is a viable alternative to the central bottleneck model.     

Involuntary attentional capture by abrupt onsets

The extent to which brief abrupt-onset visual stimuli involuntarily capture spatial attention was examined in five experiments. The paradigm used was intended to maximize the opportunity and incentive for subjects to ignore abrupt-onset distractor stimuli in nontarget locations. Subjects made a speeded two-choice response to a target letter appearing in one of four boxes. An abrupt-onset visual stimulus, easily discriminable from the target, was flashed briefly prior to the presentation of a target. In separate blocks, the flash stimulus marked the box in which the target would subsequently appear (SAME), a different box (DIFF), fixation (CENTER), or all four boxes (ALL). Prior to each block, subjects were informed of the flash-target relationship. In all five experiments, response time was elevated in the DIFF, CENTER, and ALL conditions. The interference effect was larger for the DIFF condition and persisted for longer flash-target SOAs. These results suggest that, under appropriate conditions, spatial attention can be involuntarily drawn to abrupt-onset events despite the intention of subjects’ to ignore them.     

Involuntary attentional capture by abrupt onsets.

The extent to which brief abrupt-onset visual stimuli involuntarily capture spatial attention was examined in five experiments. The paradigm used was intended to maximize the opportunity and incentive for subjects to ignore abrupt-onset distractor stimuli in nontarget locations. Subjects made a speeded two-choice response to a target letter appearing in one of four boxes. An abrupt-onset visual stimulus, easily discriminable from the target, was flashed briefly prior to the presentation of a target. In separate blocks, the flash stimulus marked the box in which the target would subsequently appear (SAME), a different box (DIFF), fixation (CENTER), or all four boxes (ALL). Prior to each block, subjects were informed of the flash-target relationship. In all five experiments, response time was elevated in the DIFF, CENTER, and ALL conditions. The interference effect was larger for the DIFF condition and persisted for longer flash-target SOAs. These results suggest that, under appropriate conditions, spatial attention can be involuntarily drawn to abrupt-onset events despite the intention of subjects' to ignore them.     

Concurrent deployment of visual attention and response selection bottleneck in a dual-task: Electrophysiological and behavioural evidence

Visual attention and response selection are limited in capacity. Here, we investigated whether visual attention requires the same bottleneck mechanism as response selection in a dual-task of the psychological refractory period (PRP) paradigm. The dual-task consisted of an auditory two-choice discrimination Task 1 and a conjunction search Task 2, which were presented at variable temporal intervals (stimulus onset asynchrony, SOA). In conjunction search, visual attention is required to select items and to bind their features resulting in a serial search process around the items in the search display (i.e., set size). We measured the reaction time of the visual search task (RT2) and the N2pc, an event-related potential (ERP), which reflects lateralized visual attention processes. If the response selection processes in Task 1 influence the visual attention processes in Task 2, N2pc latency and amplitude would be delayed and attenuated at short SOA compared to long SOA. The results, however, showed that latency and amplitude were independent of SOA, indicating that visual attention was concurrently deployed to response selection. Moreover, the RT2 analysis revealed an underadditive interaction of SOA and set size. We concluded that visual attention does not require the same bottleneck mechanism as response selection in dual-tasks.     

Time-course of Spatial-attentional Focusing in the Case of High Processing Demand on the Peripheral Precue

Subjects had to identify pairs of spatially overlapping or neighbouring letters exposed successively at various locations around the central fixation. The first letter (S1) in a pair acted both as a physical precue to indicate the S2 location and as a stimulus letter to be identified. The second letter (S2) in a pair acted only as a letter to be identified. The SOA was varied between 0 and 320 ms in different experiments. Comparison of the time-course functions of S2 identification in the conditions of (1) single pair presentation and (2) presentation of the letter pairs in the context of distractor letters that accompanied S2 in time, but occupied alternative spatial positions, revealed that S2 processing from the covert spatial-attentional focus was open to non-decreasing interference from the distractor letters up to 240 ms SOAs. An unexpected result consisted in equal level of S2 identification regardless of whether S1 had to be identified or not. This shows that if the peripheral precue has to be processed with higher processing demands at the identification level beyond simple location processing (which by itself is sufficient to fulfil the spatial orienting function), then the narrowing down or zooming-in of the attentional area in response to a physical precue can take place as effectively as in the case of a lesser processing demand on that precue. By comparing the relative time-course functions of S1 and S2 identification, it was found that S2 identification gained significant advantage over S1 identification at intermediate SOAs even if the intensity of S1 exceeded that of S2. The results of this investigation refer to the spontaneous, automatic nature of spatial attentional focusing that is evoked by spatially localised transient signals, but also to the possibility of interference between the targets and distractors in the working memory representation.     

Seeing or hearing? Perceptual independence,modality confusions,and crossmodal congruity effects with focused and divided attention

Observers were given brief presentations of pairs of simultaneous stimuli consisting of a visual and a spoken letter. In the visual focused-attention conditon, only the visual letter should be reported; in the auditory focused-attention condition, only the spoken letter should be reported; in the divided-attention condition, both letters, as well as their respective modalities, should be reported (forced choice). The proportions of correct reports were nearly the same in the three conditions (no significant divided-attention decrement), and in the divided-attention condition, the probability that the visual letter was correctly reported was independent of whether the auditory letter was correctly reported. However, with a probability much higher than chance, the observers reported hearing the visual stimulus letter or seeing the spoken stimulus letter (modality confusions). The strength of the effect was nearly the same with focused as with divided attention. We also discovered a crossmodal congruity effect: Performance was better when the two letters in a stimulus pair were the same than when they differed in type.     

The cognitive loci of the display and task-relevant set size effects on distractor interference: Evidence from a dual-task paradigm

The congruency effect of a task-irrelevant distractor has been found to be modulated by task-relevant set size and display set size. The present study used a psychological refractory period (PRP) paradigm to examine the cognitive loci of the display set size effect (dilution effect) and the task-relevant set size effect (perceptual load effect) on distractor interference. A tone discrimination task (Task 1), in which a response was made to the pitch of the target tone, was followed by a letter discrimination task (Task 2) in which different types of visual target display were used. In Experiment 1, in which display set size was manipulated to examine the nature of the display set size effect on distractor interference in Task 2, the modulation of the congruency effect by display set size was observed at both short and long stimulus-onset asynchronies (SOAs), indicating that the display set size effect occurred after the target was selected for processing in the focused attention stage. In Experiment 2, in which task-relevant set size was manipulated to examine the nature of the task-relevant set size effect on distractor interference in Task 2, the effects of task-relevant set size increased with SOA, suggesting that the target selection efficiency in the preattentive stage was impaired with increasing task-relevant set size. These results suggest that display set size and task-relevant set size modulate distractor processing in different ways.     

Localizing practice effects in dual-task performance

Practice effects on dual-task processing are of interest in current research because they may reveal the scope and limits of parallel task processing. Here we used onsets of the lateralized readiness potential (LRP), a time marker for the termination of response selection, to assess processing changes after five consecutive dual-task sessions with three stimulus onset asynchronies (SOAs) and priority on Task 1. Practice reduced reaction times in both tasks and the interference between tasks. As indicated by the LRP, the reduction of dual-task costs can be explained most parsimoniously by a shortening of the temporal demands of central bottleneck stages, without assuming parallel processing. However, the LRP also revealed a hitherto unreported early activation over the parietal scalp after practice in the short SOA condition, possibly indicating the isolation of stimulus–response translation from other central processing stages. In addition, further evidence was obtained from the LRP for a late motoric bottleneck, which is robust against practice.     

Cross-modal attentional deficits in processing tactile stimulation

In order to substantiate recent theorization on the possible links between the causes of the attentional blink and the psychological refractory period phenomena (e.g., Jolicoeur, 1999a), four experiments are reported in which two target stimuli, T1 and T2, were presented in different modalities at varying stimulus onset asynchronies (SOAs), with each stimulus being associated with a distinct task, Task1 and Task2. In Experiment 1, T1 was a tone, and Task1 was a speeded vocal response based on pitch. T2 was a brief press applied to either of two distal fingerpads, and Task2 was a speeded manual response based on tactile stimulus location. In Experiment 2, the same T1 as that used in Experiment 1 was presented, and in Task1 the subject either made a speeded vocal response based on pitch or ignored T1. T2 was a masked tactile stimulation, and Task2 was an unspeeded manual discrimination of the tactile stimulation location. This Task2 was maintained in Experiments 3 and 4. The auditory T1 was replaced with a white digit embedded in a rapid serial visualization presentation of a stream of black letters, and in Task1 the subject either made an unspeeded decision based on T1 identity or ignored T1. In all the experiments, the results showed an SOA-locked impairment in Task2. As SOA was decreased, reaction times in the speeded Task2 of Experiment 1 increased, and accuracy in the unspeeded Task2 of Experiments 2-4 decreased. The SOA-locked impairment was almost eliminated when T1 could be ignored or was absent. The results are discussed in terms of central processing limitations as the cause of such effects.     

Reading aloud is not automatic: processing capacity is required to generate a phonological code from print

The present experiments tested the claim that phonological recoding occurs "automatically" by assessing whether it uses central attention in the context of the psychological refractory period paradigm. Task 1 was a tone discrimination task and Task 2 was reading aloud. The joint effects of long-lag word repetition priming and stimulus onset asynchrony (SOA) were underadditive in Experiment 1, suggesting that an early component of lexical processing does not use central attention. In contrast, nonword letter length and grapheme-phoneme complexity yielded additive effects with SOA in Experiments 2, 3, and 4, suggesting that assembled phonology uses central attention. Further, orthographic neighborhood density also yielded additive effects with SOA in Experiments 5, 6, and 7, suggesting that lexical contributions to phonological recoding use central attention. Taken together, the results of these experiments are inconsistent with the widespread claim that phonological codes are assembled and/or addressed automatically. It is suggested that "automaticity" should be replaced by accounts that make more specific claims about how processing unfolds.     

Flank to the left,flank to the right: Testing the modified receptive field hypothesis of letter-specific crowding

The present study tested for effects of number of flankers positioned to the left and to the right of target characters as a function of visual field and stimulus type (letters or shapes). On the basis of the modified receptive field hypothesis (Chanceaux & Grainger, 2012), we predicted that the greatest effects of flanker interference would occur for leftward flankers with letter targets in the left visual field. Target letters and simple shape stimuli were briefly presented and accompanied by either 1, 2, or 3 flankers of the same category either to the left or to the right of the target, and in all conditions with a single flanker on the opposite side. Targets were presented in the left or right visual field at a fixed eccentricity, such that targets and flankers always fell into the same visual field. Results showed greatest interference for leftward flankers associated with letter targets in the left visual field, as predicted by the modified receptive field hypothesis.     

Interference effect caused by repetition in visual recognition of letters: Examination of the orthographic difference between two same letters1

Abstract: The present study examined the effect of phonological identity between two letters on the visual recognition of the letters. Participants were required to identify the two same or different letters that were successively presented for a short duration. In order to manipulate the phonological identity of the two letters, the orthography of the Kana letters was varied. In half of the trials, the first and second letters were presented in Hiragana (the same‐orthography condition). In the other half, the first letter was presented in Katakana, and the second letter in Hiragana (the different‐orthography condition). The results revealed that the identification performance for the second letter was reduced in the same‐orthography condition when the two letters were the same, compared with when they were different. In contrast to this, in the different‐orthography condition, the identification performance of the second repeated letter was marginally superior to that of the nonrepeated letter. Considering the present findings together with those of the author's previous study (Kuwana, 2004), it is suggested that the interference effect caused by repetition could result from the reduction in the availability of visual pattern information stored in long‐term memory.     

Exogenous and endogenous control of attention: the effect of visual onsets and offsets

Two experiments were carried out to investigate the relation between exogenous and endogenous control of visual attention. Subjects searched for a target letter among three nontarget letters that were positioned on an imaginary circle around a fixation point. At different cue-display intervals, a centrally located arrowhead cue reliably indicated the location of the target letter. At different SOAs, a peripheral line segment near one of the letters was either abruptly switched on (Experiment 1) or abruptly switched off (Experiment 2). Presenting the central arrowhead after display onset prevents attention from being focused in advance on the critical location. In this unfocused attentional state, both onset and offset transients attracted attention. When the central arrowhead was available in advance, the focusing of attention prior to display onset precluded attention attraction to the location of the onset or offset transient. Contrary to an offset transient, an onset transient presented at the attended location disrupted performance, indicating that an onset within the spotlight of attention attracts attention. The results are reconciled by means of the zoom-lens theory of attention, suggesting that outside the focus of attention, abrupt transients are not capable of attracting attention. Since the size of the zoom lens is under voluntary control, it can be argued that transients do not fulfill the intentionality criterion of automaticity.     

Latency dependence of word-initial letter integration by the saccadic system

Two experiments are reported in which saccadic eye movements were examined when the eyes moved to words in which the properties of the word-initial letters differed. It was found that the effect of saccade latency on landing position depended on the properties of the word-initial letters. Under short saccade latencies, landing positions deviated toward the word beginning in the presence of orthographically irregular/informative beginning (OI/IB) letters. This result is interpreted as an influence of the orthographic encoding process that has detected an unusual letter grouping. With longer saccade latencies, an increase of the saccade size was observed for OI/IB words, whereas orthographically regular/uninformative beginning words did not show the effect. It is suggested that this may be a consequence of the dynamics of parafoveal word information processing.     

Localizing practice effects in dual-task performance

Practice effects on dual-task processing are of interest in current research because they may reveal the scope and limits of parallel task processing. Here we used onsets of the lateralized readiness potential (LRP), a time marker for the termination of response selection, to assess processing changes after five consecutive dual-task sessions with three stimulus onset asynchronies (SOAs) and priority on Task 1. Practice reduced reaction times in both tasks and the interference between tasks. As indicated by the LRP, the reduction of dual-task costs can be explained most parsimoniously by a shortening of the temporal demands of central bottleneck stages, without assuming parallel processing. However, the LRP also revealed a hitherto unreported early activation over the parietal scalp after practice in the short SOA condition, possibly indicating the isolation of stimulus-response translation from other central processing stages. In addition, further evidence was obtained from the LRP for a late motoric bottleneck, which is robust against practice.