Task- and location-switching effects on visual attention

In two experiments, we examined the effects of task and location switching on the accuracy of reporting target characters in an attentional blink (AB) paradigm. Single-character streams were presented at a rate of 100 msec per character in Experiment 1, and successive pairs of characters on either side of fixation were presented in Experiment 2. On each trial, two targets appeared that were either white letters or black digits embedded in a stream of black letter distractors, and they were separated by between zero and five items in the stream (lags 1-6). Experiment 1 showed that report of the first target was least accurate if it immediately preceded the second target and if the two targets were either both letters or both digits (task repetition cost). Report of the second target was least accurate if one or two distractors intervened between the two targets (the U-shaped AB lag effect) and if one target was a letter and the other a digit (task switch cost). Experiment 2 added location uncertainty as a factor and showed similar effects as Experiment 1, with one exception. Lag 1 sparing (the preserved accuracy in reporting the second of two targets if the second immediately follows the first) was completely eliminated when the task required attention switching across locations. Two-way additive effects were found between task switching and location switching in the AB paradigm. These results suggests separate loci for their attentional effects. It is likely that the AB deficit is due mainly to central memory limitations, whereas location-switching costs occur at early visual levels. Task-switching costs occur at an intermediate visual level, since the present task switch involved encoding differences without changes in stimulus-response mapping rules (i.e., the task was character identification for both letters and digits).     

Effect of lateralized gaps in noise on the cutaneous blink reflex in humans

The early (R1) and late (R2) components of the cutaneous blink reflex in right-handed humans were recorded in three experiments to examine the lateral symmetry of a simple excitatory process in their brainstem pathways and of the control of the excitability of the pathways by gaps in acoustic noise. Experiment 1 showed that a stimulus below R1-elicitation threshold increased the excitability of the right R1 pathway more than the left but that the rate of decay was similar on both sides. Experiment 2 showed that a brief unilateral gap in noise affected the R1 and R2 reflex pathways bilaterally. Experiment 3 showed that R2 varied with gap duration and that gaps to the left and right ears had indistinguishable effects. The finer temporal resolution of events in the right sensory field of right-handers seen in psychophysical judgments is not seen in the descending control of brainstem excitability.     

On the labile memory buffer in the attentional blink: masking the T2 representation by onset transients mediates the AB

Report of a second target (T2) is impaired when presented within 500 ms of the first (T1). This attentional blink (AB) is known to cause a delay in T2 processing during which T2 must be stored in a labile memory buffer. We explored the buffer's characteristics using different types of masks after T2. These characteristics were inferred by determining what attributes of T2 are hindered by a given form of masking. In Experiments 1-3, trailing metacontrast and four-dot masks produced ABs of equal magnitudes, implicating the onset-transient triggered by the mask as the mechanism underlying the AB and strongly suggesting a locus in early vision. In Experiment 4, metacontrast and four-dot masks were presented in a common-onset masking (COM) paradigm in which a brief, combined display of T2 and the mask was followed by a longer display of the mask alone. COM is thought to occur late in the sequence of processing events. No AB occurred with COM, confirming the critical role of the mask's onset transients and ruling out a high-level locus for the labile memory buffer.     

Attentional limitations in processing sequentially presented vibrotactile targets

In seven experiments, participants experienced rapid, serially presented streams of vibrations and responded to specific targets in the streams. In visual (and sometimes auditory) streams presented in this manner, it is typical to find a deficit in reporting the second of two targets when both must be reported and the second appears within a short temporal interval of the first, but not when identical displays are presented but only the second target must be reported (e.g., the attentional blink, or AB). This conventional AB pattern was found in the last experiment, in which judgments were about target location. However in the first six experiments reported here, in which judgments were about frequency, intensity, duration, or location of targets, accuracy was dependent on target separation regardless of whether or not the first target was reported. This unconventional pattern could represent an AB if the first target was attended even when it was not reported. The evidence for this claim and an alternative possibility that location judgments are especially sensitive to attention manipulations are discussed.     

The role of observer strategy in the single-target AB paradigm

Identification of the second of two targets (T1, T2) inserted in a stream of distractors is impaired when presented 200–500 ms after the first (attentional blink, AB). An AB-like effect has been reported by Nieuwenstein, Potter, and Theeuwes, Journal of Experimental Psychology: Human Perception and Performance, 35, 159-169, (2009, Experiment 2), with a distractor stream that contained only one target and a gap just before the target. Nieuwenstein et al. hypothesized that the gap enhanced the salience of the last distractor, causing it to be processed much like T1 in conventional AB studies. This hypothesis can also account for Lag-1 sparing (enhanced target performance when presented directly after the last distractor, without an intervening gap). We propose an alternative account of the Lag-1 sparing in the single-target paradigm based on observer strategy, and test it by presenting the single-target and dual-target conditions to separate groups (Experiment 2) instead of mixed across trials (Experiment 1 and Nieuwenstein et al.'s study). The single-target condition exhibited Lag-1 sparing when it was mixed with the dual-target condition, but Lag-1 deficit when it was done in isolation. This outcome is consistent with an observer-strategy account but not with an enhanced salience account of the Lag-1 sparing effect in the single-target condition.     

Judgments of duration, figure-ground contrast, and size for words and nonwords

Does the word-superiority effect on letter discrimination result in a word-superiority effect on duration judgments? We examined this question in five experiments. In the first four experiments, we have demonstrated that (1) words shown for 32-80 msec were judged as presented longer than non-words shown for the same duration; (2) this word-superiority effect persists if the stimuli are shown for an objective duration of up to 250 msec; and (3) these effects can be extended to judgments of figure-ground contrast and letter size. These findings extend existing data on effects of processing fluency on perceptual judgments. In Experiment 5, we found that duration judgments were higher for words than for pronounceable nonwords, and duration judgments were higher for pronounceable non-words than for nonpronounceable nonwords. We discuss the implications of this finding for the discrepancy-attribution hypothesis.     

The effect of target contrast on the attentional blink

In this set of five rapid serial visual presentation experiments, observers identified one or two target letters that were embedded in a stream of distractors. Target contrasts were varied, and their effects on the attentional blink (AB) were examined. Target identification improved when its contrast was increased. But whereas an increase in the first target's (T1) contrast facilitated its identification, the recovery of the second target (T2) was paradoxically hampered (Experiments 2 and 5). Similarly, identification of the target suffered when the preceding singleton's contrast was increased (Experiment 1). The AB was eliminated by inserting a blank after a low-contrast, but not a high-contrast, T1 (Experiment 5). Increasing T2's contrast attenuated the blink (Experiment 3) and compensated the larger AB caused by a high-contrast T1 (Experiment 4). In all, these results showed that attention continued to be engaged as long as the target's contrast prolonged its perceptibility. When the high-contrast target was T1, a larger AB was produced; when it was T2, there was protection from substitution masking.     

The attentional blink is susceptible to concurrent perceptual processing demands

In a rapid serial visual presentation stream processing of a first target (T1) impairs detection or identification of a second target (T2) that appears within 500 ms after T1. This effect characterizes the so-called attentional blink (AB). To evaluate contemporary information-processing accounts of the AB phenomenon in terms of the underlying processing mechanisms the present study examined the potential influence of Task 1 difficulty on the AB effect. To this end, T1 contrast and T1 response requirements were systematically varied across four experiments. Experiment 1 ruled out a mere sensory basis of the contrast manipulation on T2 performance. When only T2 had to be reported (Experiment 2) an AB effect occurred that was slightly modulated by T1 contrast. When report of both T1 and T2 was required in a standard AB task (Experiment 3), the magnitude of the AB depended to a larger extent on stimulus contrast, and it increased further when speeded T1 choice responses were additionally required (Experiment 4). On the basis of the present impact of Task 1 difficulty on the AB effect we conclude that processing limitations cause the AB phenomenon. We discuss such limitations in terms of perceptual (T1 consolidation) and central (response selection) bottleneck processes.     

Alerting enhances target identification but does not affect the magnitude of the attentional blink

Identification of the second of two targets is impaired when presented less than about 500 ms after the first. The magnitude of this attentional blink (AB) is known to be modulated by tonic factors (e.g., observer's state of relaxation). The present work examined the effects of a phasic change in observer's state brought about by an alerting stimulus (an aggregate of faint rings) presented in temporal proximity to either letter-target inserted in a temporal stream (RSVP) of digit distractors. In four experiments, identification accuracy of each target was substantially improved by presenting the alerting stimulus either in the target's frame or in the preceding RSVP frame. However, alerting did not modulate the magnitude of the AB. The appearance of an alerting effect on the AB in Experiment 1 was ascribed to a ceiling effect in Experiment 2. Experiment 3 ruled out endogenous temporal cueing effects; Experiment 4 examined the temporal gradient of alerting. Independence of the alerting and AB effects suggests that the alerting stimuli and the letter targets may be processed along distinct visual pathways.     

Dissociating the effects of featural and conceptual interference on multiple target processing in rapid serial visual presentation

Attentional blink (AB) describes the finding that, when subjects attend to a specified target in a rapidly presented visual stream, they show a decreased ability to process a subsequent probe item for up to 600 msec. In the present study, the roles of featural and conceptual interference in the processing of targets and probes in a rapid serial visual presentation stream were examined. In Experiment 1, featurally more complex T + 1 items produced larger AB even when the physical energy of the stimulus (e.g., the number of pixels) was held constant. In Experiment 2, the conceptual category of the T + 1 item affected target identification but not AB magnitude. These result suggest that featural interference is a major determinant of AB magnitude, whereas featural and conceptual interference both affect target identification.     

Interval timing with gaps: gap ambiguity as an alternative to temporal decay

C. V. Buhusi, D. Perera, and W. H. Meck (2005) proposed a hypothesis of timing in rats to account for the results of experiments that have used the peak procedure with gaps. According to this hypothesis, the introduction of a gap causes the animal's memory for the pregap interval to passively decay (subjectively shorten) in direct proportion to the duration and salience of the gap. Thus, animals should pause with short, nonsalient gaps but should reset their clock with longer, salient gaps. The present authors suggest that the ambiguity of the gap (i.e., the similarity between the gap and the intertrial interval in both appearance and relative duration) causes the animal to actively reset the clock and prevents adequate assessments of the fate of timed intervals prior to the gap. Furthermore, when the intertrial interval is discriminable from the gap, the evidence suggests that timed intervals prior to the gap are not lost but are retained in memory.     

Internal clock processes and the filled-duration illusion

In 3 experiments, the authors compared duration judgments of filled stimuli (tones) with unfilled ones (intervals defined by clicks or gaps in tones). Temporal generalization procedures (Experiment 1) and verbal estimation procedures (Experiments 2 and 3) all showed that subjective durations of the tones were considerably longer than those of unfilled intervals defined either by clicks or gaps, with the unfilled intervals being judged as approximately 55%-65% of the duration of the filled ones when real duration was the same. Analyses derived from the pacemaker-switch-accumulator clock model incorporated into scalar timing theory suggested that the filled/unfilled difference in mean estimates was due to higher pacemaker speed in the former case, although conclusively ruling out alternative interpretations in terms of attention remains difficult.     

Adjusting fixed-ratio schedules in the squirrel monkey

On an adjusting schedule of reinforcement, a parameter of the schedule is varied as a function of some characteristic of the animal's performance. In Experiment I, the fixed-ratio response requirement was varied as a function of the time that elapsed before the animal started responding in each fixed-ratio (initial pause). When initial pauses were shorter than a specified duration, the response requirement was increased; when they were longer than the specified duration, the response requirement was decreased. Specified durations of 1, 2, 4, 8, and 15 min were studied. The average response requirement maintained by each monkey was directly related to the length of the specified duration of initial pause. In Experiment II, the fixed-ratio response requirement was constant, but reinforcement occurred only when the initial pause was longer than a specified duration. The average durations of initial pauses were directly related to the length of the specified duration and to the response requirement. Meprobamate consistently decreased the average durations of initial pauses.     

Attentional capture triggers an attentional blink

Two experiments examined the possibility that attention directed to a distractor during rapid serial visual presentation (RSVP) can produce an attentional blink (AB). A to-be-ignored distractor (D1) preceded a target word (T2) by a variable lag in RSVP streams of black false-font distractors. D1 was highlighted by color and was a word, a string of consonants, a string of digits, or a string of false-font characters. Recall of T2 was significantly suppressed at short D1-T2 lags (the AB) but only when D1 contained letters; the AB was completely absent when D1 was composed of digits or false-font characters. Thus, the AB can be triggered by a highlighted distractor if the distractor shares features with a target.     

Spelling-to-sound regularity affects pronunciation latency but not lexical decision

Summary A series of experiments are reported concerning the regularity effect in single- word pronunciation and lexical decision tasks. Experiment 1 compared pronunciation latencies for exception words based on unfamiliar letter patterns (e.g., YACHT) with exception words based on common letter patterns (e.g., PINT). It was found that both types of exceptions produced longer latencies than regular words. Experiment 2 employed a more objective basis for matching exception and regular words for letter pattern familiarity. Under these conditions exception words still produced significantly longer pronunciation latencies than regular words. These experiments show that previous demonstrations of the regularity effect in pronunciation cannot be attributed to uncontrolled visual differences between exception and regular words. Experiment 3 investigated whether the same material as Experiment 2 would produce a regularity effect in lexical decision but this was not found. Theoretical implications of these resuts and discrepancies with previous studies are discussed.     

The “beam of darkness”: Spreading of the attentional blink within and between objects

When two targets (T1 and T2) are inserted into a rapid serial visual presentation (RSVP) stream of nontargets, observers are impaired at identifying T2 when it is presented within half a second after T1. This transient drop in performance, or attentional blink (AB), has been attributed to a temporary unavailability of task-critical processing resources. In the present study, we investigated how object-based attention modulates the AB, by presenting four synchronized RSVP streams in the corners of two rectangular bars (e.g., one above and one below fixation). The results from four experiments revealed that the AB increased within short temporal lags (of up to ～400 msec) when T2 was presented on the same, rather than a different, bar as T1 (with T1–T2 spatial distance controlled for). Thus, the AB is seen to spread across entire object groupings, suggesting that the spatiotemporal resolution of attention is modulated by global-object information.     

Upshifted decision criteria in attentional blink and repetition blindness

A large number of “unawareness” phenomena have been explained and quantified in terms of sensitivity (d′) fluctuations, with very few attempts at addressing an alternative putative cause, i.e., fluctuations of subjects’ response criteria (c). Response criteria fluctuations are particularly likely under dual-task paradigms with unbalanced sensitivities (Gorea & Sagi, 2000) such as those used in evidencing attentional blink (AB) and repetition blindness (RB) phenomena. The present study inquires into whether AB and RB are indeed prone to a deviant decisional behaviour. AB and RB were studied with a yes/no task allowing the assessment of d′ and c for the detection (presence/absence) of a target letter T2 as a function of its temporal lag relative to the presentation of another (AB) or of the same (RB) letter, T1 (Experiment 1). A significant criterion increase was observed in both cases. Additional experiments demonstrate that this criterion effect is typical of these dual-task AB and RB paradigms as it is not observed in a standard contrast detection task with mixed contrasts (Experiment 2), in a “control” AB design stripped off its first task T1 (Experiment 3), or in a metacontrast experiment (Experiment 4). We propose that the observed criterion shifts are the consequence of the inherent dual-task AB and RB designs (where observers have to judge two events of unequal saliencies) and that they entail an enhancement of the AB and RB effects as long as these effects are assessed via subjective (yes/no or matching) procedures.     

Symbolic control of attention: Tracking its temporal dynamics

Three experiments examined the temporal dynamics of the impact of symbols with task-irrelevant spatial meanings on attentional control. In Experiments 1 and 2, participants were color-cued to report the first letter they saw in the left or right of two parallel letter streams. The cue appeared in the shape of an arrow pointing to the target stream (compatible) or to the other stream (incompatible). Incompatible arrows delayed letter selection; that is, participants reported later-appearing letters and made more errors. In Experiment 3, the target stream was cued in advance, and yet, incompatible symbols delayed target selection. These findings suggest that the irrelevant meaning of symbolic stimuli can still penetrate and bias attentional top-down control, an observation that challenges available control theories.     

Attentional blink for color

Colored letters were presented by means of rapid serial visual presentation (RSVP). Two letters (T1 and T2) were targets that required a speeded (T1) or delayed (T2) response. T1 was shown on half of the trials. Two tasks were performed in the experimental conditions. Task 1 required a discrimination between 2 letters (when T1 was shown) or an indication that T1 was absent. In Experiment 1, Task 2 was to detect the presence of a unique color in the RSVP stream (e.g., green in a stream of alternating red and gray). In Experiment 2, Task 2 was to report the color of the first colored letter to appear in the RSVP stream. The lag between T1 and T2 in the RSVP stream was manipulated. Accuracy of color reports in Task 2 was poor at shorter lags and improved as the lag was lengthened in both experiments, demonstrating an attentional blink for chromatic information. Theoretical implications of the results are discussed.     

Reflex inhibition in humans: Sensitivity to brief silent periods in white noise

A white noise (60 dB SPL) was always present except for brief silent periods (“gaps”) which occurred just before an eyelid reflex was elicited in human volunteers by a brief innocuous shock to the forehead. In Experiment 1 (n=8), 10-msec gaps (“S1”) were given 40, 80, 120, 160, or 200 msec before the shock (“S2”). Compared with S2-alone trials, the reflex was inhibited by about 50% at intervals of 80 msec and beyond. Experiment 2 (n=12) first provided detection thresholds for gaps using a simple version of the method of limits: on average a gap of 5.4 msec duration was just detected. Then gaps of 0, 2, 4, 6, 8, and 10 msec were given in random order, each 100 msec before S2. The 4-msec stimulus was an effective inhibitor of the reflex, and inhibition further increased on to 6- and then to 8-msec durations. A comparison of the values obtained on reflex inhibition with the 5.4-msec threshold obtained with the conventional psycho-physical test reveals that in humans reflex inhibition provides an objective index of stimulus detection that is at least of sufficient sensitivity to warrant its clinical application. The steady increase in reflex inhibition as gap duration increased from 2 to 8 msec may be of significance for tracing the rate of decay of afferent stimulation following noise offset, as it presumably reflects the growing sensitivity to the resumption of the noise as the duration of the silent period is increased.