T1 difficulty and the attentional blink: expectancy versus backward masking

According to bottleneck models of the attentional blink (AB), first-target (T1) processing difficulty should be related to AB magnitude. Tests of this prediction that have varied T1 difficulty in the context of a standard AB paradigm, however, have yielded mixed results. The present work examines two factors that may mediate the relationship between T1 difficulty and the AB: observer expectancy and backward masking of T1. In two experiments, omission of the backward mask consistently yielded the predicted relationship between T1 difficulty and the AB. In contrast, observer expectancy influenced target identification accuracy but did not mediate the relationship between T1 difficulty and the AB.     

Task switching mediates the attentional blink even without backward masking

When two targets are presented in rapid succession, perception of the second target is impaired at short intertarget lags (100-700 msec). This attentional blink (AB) is thought to occur only when the second target is backward masked. To the contrary, we show that task switching between the targets can produce an AB even without masking (Experiments 1 and 3). Further, we show that task switching produces an AB only when the second target does not belong to a class of overlearned stimuli such as letters or digits (Experiments 1 and 4). When the second target is masked, however, an AB is invariably obtained regardless of switching or overlearning. We propose that task switching involves a time-consuming process of reconfiguration of the visual system, during which the representation of the second target decays beyond recognition, resulting in an AB deficit. We suggest that overlearned stimuli are encoded in a form that, while maskable, decays relatively slowly, thus outlasting the delay due to reconfiguration and avoiding the AB deficit.     

Neither backward masking of T2 nor task switching is necessary for the attentional blink

Identification of the second of two targets (T1, T2, inserted in a stream of distractors) is impaired when presented within 500 ms after the first (attentional blink, AB). Barring a T1-T2 task-switch, it is thought that T2 must be backward-masked to obtain an AB (Giesbrecht &; Di Lollo, Journal of Experimental Psychology: Human Perception and Performance, 24, 1454-1466, 1998). We tested the hypothesis that Giesbrecht &; Di Lollo's findings were vitiated by ceiling constraints arising from either response scale (experiment 1) or data limitations (experiment 2). In experiment 1, digit-distractors were replaced with pseudoletters to increase task difficulty, bringing performance below ceiling. An AB occurred without backward masking of T2. In experiment 2, a ceiling-free procedure estimated the number of noise dots needed for 80% T2 identification. An AB was revealed: fewer noise dots were required during the AB period than outside it. Both outcomes confirm that an AB can be obtained without either masking of T2 or task switching.     

Data-limited manipulations of T1 difficulty modulate the attentional blink.

When two targets are embedded in a temporal stream of distractors, second-target identification is initially impaired and then gradually improves as intertarget interval lengthens (attentional blink; AB). According to bottleneck models of the AB, difficulty of first-target processing should modulate the magnitude of the second-target deficit. To test this, we examined whether a data-limited manipulation of T1 difficulty (forward masking) would modulate AB magnitude. In two experiments, we show that data-limited manipulations of T1 difficulty do affect the AB, so long as T1 is not masked by an immediately trailing distractor. When such a trailing item is present, the relationship between T1 difficulty and the AB disappears.     

Representational masking and the attentional blink

After successful detection of a target item within a stream of rapidly displayed visual stimuli, subsequent detection of an additional target is impaired for roughly 500 ms. This impairment is known as the “attentional blink” (AB). Previous studies have found that if either the first (Tl; Raymond, Shapiro, & Arnell, 1992) or second target (T2; Giesbrecht & Di Lollo, 1998) is not followed by a mask, the AB impairment is significantly reduced. Whereas low-level perceptual factors have been found to influence the efficacy of masking in the AB (e.g., Seiffert & Di Lollo, 1997), the current experiment used a higher level (representational) manipulation, i.e., repetition blindness to reduce the efficacy of target masking in the AB. These findings contribute to the growing literature suggesting that masking plays more than a perceptual role in the AB phenomenon.     

Beyond Task 1 difficulty: The duration of T1 encoding modulates the attentional blink

Manipulations of Task 1 difficulty in the attentional blink paradigm can have minimal effects on performance of a subsequent visual encoding task, when Task 1 difficulty is thought of as a form of data limitation (e.g., by masking T1 more or less effectively) using mixed trials (e.g., McLaughlin, Shore, & Klein, 2001). In this work we show that a different form of Task 1 difficulty, namely the difficulty of organizing T1 as a representation in STM, has a large impact on accuracy in Task 2, even when the different levels of Task 1 difficulty are intermixed from trial to trial. The results support the Central Interference Theory of the attentional blink by showing that the time taken for central processing of T1 has a direct impact on performance in Task 2.     

Variations in backward masking with different masking stimuli: I. Local interaction versus attentional switch

The types of stimuli used as targets and masks considerably change the masking functions in a way that requires us to abandon any single mechanism of masking as the sole explanation of backward masking. In the first of two reports in which the problem of the mask-dependence of masking is addressed, we explore the role of the relative spatial positioning of targets and masks in order to differentiate between local interaction and attentional models. If single letters were masked by double-letter masks then the relative spatial arrangement of the letters, which was changed in order to vary the involvement of metacontrast-like processes, had an effect at shorter SOAs, but not at longer SOAs where strong masking still persisted. This poses difficulties for proposing local contour interaction as the main mechanism of masking. Similarly, crowding effects alone cannot explain the results. Backward masking also involves attention being directed to working-memory processing of the succeeding object while abandoning the preceding object.     

The attentional blink is not affected by backward masking of T2, T2-mask SOA, or level of T2 impoverishment

Identification of the second of two targets (T2) is impaired when presented shortly after the first (T1). This attentional blink (AB) is thought to arise from a delay in T2 processing during which T2 is vulnerable to masking. Conventional studies have measured T2 accuracy which is constrained by the 100% ceiling. We avoided this problem by using a dynamic threshold-tracking procedure that is inherently free from ceiling constraints. In two experiments we examined how AB magnitude is affected by three masking-related factors: (a) presence/absence of T2 mask, (b) T2-mask stimulus onset asynchrony (SOA), and (c) level of T2 impoverishment (signal-to-noise ratio [SNR]). In Experiment 1, overall accuracy decreased with T2-mask SOA. The magnitude of the AB, however, was invariant with SOA and with mask presence/absence. Experiment 2 further showed that the AB was invariant with T2 SNR. The relationship among mask presence/absence, SOA, and T2 SNR and the AB is encompassed in a qualitative model.     

Masking T1 difficulty: processing time and the attenional blink

When observers are presented with 2 targets in rapid succession, identification of the 1st is highly accurate, whereas identification of the 2nd is impaired at brief intertarget intervals (i.e., 200-500 ms). This 2nd-target deficit is known as the attentional blink (AB). According to bottleneck models, the AB arises because attending to the 1st target delays allocation of attention to the 2nd target. Thus, these models predict that increasing 1st-target processing time will increase the magnitude of the AB. Previous tests of this prediction have yielded mixed results. The present work suggests that one factor contributing to this uncertainty is masking of the 1st target: When this mask is omitted, processing time and AB magnitude are reliably related. These findings clarify the role of 1st-target masking in the AB and support the validity of the bottleneck account.     

Visual masking plays two roles in the attentional blink

When two targets are displayed in rapid visual sequence and masked by trailing patterns, identification accuracy is nearly perfect for the first target but follows a U-shaped pattern over temporal lag for the second target. Three experiments examined the role of visual masking in this attentional blink. Experiment 1 compared integration and interruption masks for both targets. Although either mask was effective in producing the blink when applied to the first target, only the interruption mask was effective when applied to the second target. Experiment 2 showed that integration masking of the second target was ineffective over a wide range of accuracy levels. Combining the two forms of masking in Experiment 3 confirmed the dissociation: A combined mask and only a main effect on accuracy for the first target, whereas it produced a qualitatively different pattern over temporal lag for the second target. These results suggest that representations of the target are substituted in consciousness by that of the interruption mask when visual attention is preoccupied.     

Auditory attentional blink: masking the second target is necessary, delayed masking is sufficient.

When two target items (T1 and T2) are presented in rapid succession among fillers, processing T2 is often impaired. This phenomenon is known as the attentional blink (AB). Within the visual modality, this second-target deficit generally occurs only if T2 is masked by a trailing item. The current study was designed to examine whether masking of T2 also plays a critical role in the auditory AB. Results showed a reliable AB effect even when the item following T2 was replaced by silence. However, the AB deficit was abolished when T2 was the last presented stimulus. Our results suggest that, as in vision, T2 masking is necessary for the AB to take place in audition, but that masking is effective even when delayed, providing evidence that the phenomenon shares some functional mechanisms across sensory modalities.     

Short-term memory and the attentional blink: Capacity versus content

When people monitor the rapid serial visual presentation (RSVP) of stimuli for two targets (T1 and T2), they often miss T2 if it falls into a time window of about half a second after T1 onset, a phenomenon known as the attentional blink (AB). We found that overall performance in an RSVP task was impaired by a concurrent short-term memory (STM) task and, furthermore, that this effect increased when STM load was higher and when its content was more task relevant. Loading visually defined stimuli and adding articulatory suppression further impaired performance on the RSVP task, but the size of the AB over time (i.e., T1-T2 lag) remained unaffected by load or content. This suggested that at least part of the performance in an RSVP task reflects interference between competing codes within STM, as interference models have held, whereas the AB proper reflects capacity limitations in the transfer to STM, as consolidation models have claimed.     

Visual masking during the attentional blink: tests of the object substitution hypothesis

When 2 masked targets are presented in a rapid sequence, correct identification of the 1st hinders identification of the 2nd. Visual masking of the 2nd target plays a critical role during this 2nd-target deficit, or "attentional blink" (AB). The object substitution hypothesis (B. Giesbrecht & V. Di Lollo, 1998) predicts that late-stage visual processes involved in object substitution mediate masking of the 2nd target during AB, whereby stronger masking should produce a more severe deficit. Six experiments are presented, together testing this hypothesis. Although masking by object substitution was observed, it did not interact with the AB. An alternative hypothesis is proposed stating that mostly early-stage visual processes mediate the masking effects that are critical to the AB.     

The roles of location specificity and masking mechanisms in the attentional blink

In a series of four experiments using rapid serial visual presentations of two target letters embedded in numeral distractors, with different numbers of display positions and with or without masking, we show that (1) the nonmonotonic, U-shaped attentional blink (AB) function, which occurs when all items are presented at the same display location, is eliminated in favor of a monotonic function when targets and distractors are presented randomly dispersed over four or nine adjacent positions; (2) the AB monotonicity is maintained with the spatially distributed presentation even when backward masks are used in all possible stimulus positions and when the location of the next item in sequence is predictable; and (3) the If-shaped AB is not due to position-specific forward or backward masking effects occurring at early levels of visual processing. We tentatively conclude that the U-shaped AB is primarily a function of the interruption of late visual processing produced when the item following the first target occurs at the same location. In order for the AB to severely disrupt performance, the item following the first target must be presented at the same location as the target so that it can serve both as a distractor and as a mask interrupting or interfering with subsequent visual processing.     

The roles of location specificity and masking mechanisms in the attentional blink.

In a series of four experiments using rapid serial visual presentations of two target letters embedded in numeral distractors, with different numbers of display positions and with or without masking, we show that (1) the nonmonotonic, U-shaped attentional blink (AB) function, which occurs when all items are presented at the same display location, is eliminated in favor of a monotonic function when targets and distractors are presented randomly dispersed over four or nine adjacent positions; (2) the AB monotonicity is maintained with the spatially distributed presentation even when backward masks are used in all possible stimulus positions and when the location of the next item in sequence is predictable; and (3) the U-shaped AB is not due to position-specific forward or backward masking effects occurring at early levels of visual processing. We tentatively conclude that the U-shaped AB is primarily a function of the interruption of late visual processing produced when the item following the first target occurs at the same location. In order for the AB to severely disrupt performance, the item following the first target must be presented at the same location as the target so that it can serve both as a distractor and as a mask interrupting of interfering with subsequent visual processing.     

Delayed masking and the auditory attentional blink: A test for retrieval competition and bottleneck models

The attentional blink (AB) corresponds to a transient deficit in reporting the second (T2) of two targets embedded in a rapid sequence of distractors. The retrieval competition (Shapiro, Raymond & Arnell, 1994) and bottleneck models (Chun & Potter, 1995; Jolicoeur, 1998) predict the attenuation of the deficit with the extension of the delay between T2 and its mask. This prediction was tested using auditory sequences of nonverbal stimuli in which the T2-mask interval was systematically varied. The magnitude of the auditory AB diminished with the lengthening of the interval from 50 to 150 ms while no time-locked deficit was observed with the longest (350 ms) and the shortest (10 ms) intervals. These results suggest that presenting a mask after T2 is not sufficient to produce an auditory AB: The mask must be perceivable as an auditory event distinct from the target and occur before T2 consolidation. The present study also provides evidence that as in vision, AB deficits take place in the auditory domain when T2 is masked by interruption but not by integration. Our findings are best accounted for in terms of bottlenecked processing limitations.     

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.     

Eye movements blink the attentional blink

When presented with a sequence of visual stimuli in rapid succession, participants often fail to detect a second salient target, a phenomenon referred as the attentional blink (AB; Raymond, Shapiro, & Arnell, 1992; Shapiro, Raymond, & Arnell, 1997). On the basis of a vast corpus of experiments, several cognitive theories suggest that the blink results from a discrete structuring of attention, sampling information from temporal episodes during which several items can access encoding process (Wyble, Bowman, & Nieuwenstein, 2009; Wyble, Potter, Bowman, & Nieuwenstein, 2011). The objective of this work is to explore the AB when multiple items are presented at the fovea during ocular movements. The authors reasoned that each fixation may cohesively form an episode and hence expected that the blink may vanish within a single fixation. In turn, they expected saccades to accentuate episodic borders and hence shorten the regime of interference when 2 targets are presented fovealy in successive fixations. Evidence is provided in favor of this hypothesis, showing that the blink vanishes when both targets are presented in the core of a single fixation (far from the saccadic boundaries) and that it recovers more rapidly in successive fixations. These studies support current views that episodes should have an effect on the AB and provide evidence that eye movements play an important role in the formation of episodes.