The efficiency of encoding: limits of information transfer into memory

We investigated how visual information is best presented to maximize the number of remembered items in a fixed time unit. In a memory task for images depicting real-world objects, we varied the number of images shown simultaneously, the presentation time, and the interstimulus interval (ISI). The viewing phase was followed by a two-alternative forced choice recognition task. We converted the percentage of correct answers into a capacity estimate scaled to a fixed time unit of 1 s to allow for comparisons across conditions. Our results showed that (1) presenting one image very briefly was always more efficient than simultaneously showing multiple images for longer periods; (2) for single images, the maximum encoding rate was fairly constant over a wide range of conditions, at 1.4 objects per second; (3) when testing was done a week later, memory capacity was the same for all conditions, irrespective of the presentation time and ISI at the initial viewing; (4) highly similar distractors led to worse performance than random distractors; and (5) showing an image twice for 100 ms was associated with worse performance than showing the image once, but for 200 ms.     

工作记忆表征精度加工需求对注意引导的影响

采用注意捕获范式, 通过行为和事件相关脑电位(ERP)实验, 探讨工作记忆表征精度加工需求对注意引导的影响, 行为结果发现, 在低精度加工需求条件下, 只有一个工作记忆表征引导注意, 且处于高激活状态的工作记忆表征产生的注意捕获大于低激活状态; 而在高精度加工需求条件下, 有两个工作记忆表征引导注意, 且处于高、低激活状态的工作记忆表征产生的注意捕获没有差异。ERP结果显示, 高精度加工需求条件下诱发的NSW和LPC大于低精度加工需求条件; 在高精度加工需求条件下, 干扰项与记忆项匹配比不匹配时, 诱发更大的N2和更小的N2pc, 而在低精度加工需求条件下, 干扰项与记忆项匹配和不匹配时诱发的N2、N2pc没有差异。研究表明, 工作记忆表征精度加工需求影响注意引导的机制可能是高精度加工需求下, 工作记忆表征消耗的认知资源增加, 搜索目标获得的资源减少, 干扰项捕获的注意增加。     

Phonological encoding in the attentional blink paradigm

The attentional blink refers to a deficit in reporting a second target that follows a first target within a few hundred milliseconds, when both targets occur in a sequence of distractors shown serially at rates of about 10 items per second. In four experiments, phonological similarity of post-Target 1 distractors impaired dual target report within the interval in which the attentional blink occurs. Similarity of letter targets had a smaller, less reliable effect on performance. Phonological similarity of letter distractors did not affect single target identification (Experiment 3), but it continued to impair dual target report (Experiment 5), even when the targets belonged to a different category—namely, digits. The results demonstrated that, not only targets, but also distractors are encoded phonologically, despite the fact that distractors are irrelevant and never have to be reported.     

Extracting thresholds from noisy psychophysical data.

Psychophysical studies with infants or with patients often are unable to use pilot data, training, or large numbers of trials. To evaluate threshold estimates under these conditions, computer simulations of experiments with small numbers of trials were performed by using psychometric functions based on a model of two types of noise: stimulus-related noise (affecting slope) and extraneous noise (affecting upper asymptote). Threshold estimates were biased and imprecise when extraneous noise was high, as were the estimates of extraneous noise. Strategies were developed for rejecting data sets as too noisy for unbiased and precise threshold estimation; these strategies were most successful when extraneous noise was low for most of the data sets. An analysis of 1,026 data sets from visual function tests of infants and toddlers showed that extraneous noise is often considerable, that experimental paradigms can be developed that minimize extraneous noise, and that data analysis that does not consider the effects of extraneous noise may underestimate test-retest reliability and overestimate interocular differences.     

Specific phonological impairments in dyslexia revealed by eyetracking

Phonological deficits in dyslexia are typically assessed using metalinguistic tasks vulnerable to extraneous factors such as attention and memory. The present work takes the novel approach of measuring phonology using eyetracking. Eye movements of dyslexic children were monitored during an auditory word recognition task in which target items in a display (e.g., candle) were accompanied by distractors sharing a cohort (candy) or rhyme (sandal). Like controls, dyslexics showed slower recognition times when a cohort distractor was present than in a baseline condition with only phonologically unrelated distractors. However, unlike controls, dyslexic children did not show slowed recognition of targets with a rhyme distractor, suggesting they had not encoded rhyme relationships. This was further explored in an overt phonological awareness test of cohort and rhyme. Surprisingly, dyslexics showed normal rhyme performance but poorer judgment of initial sounds on these overt tests. The results implicate impaired knowledge of rhyme information in dyslexia; however they also indicate that testing methodology plays a critical role in how such problems are identified.     

On the fate of distractor stimuli in rapid serial visual presentation

Observers demonstrate an impaired ability to report the second of two targets in a rapid serial visual presentation (RSVP) stream if it appears within 500 ms of the first target--a phenomenon known as the attentional blink. This study investigated the fate of stimuli in dual-target RSVP streams that do not require report--the distractors. In five experiments, observers viewed dual-target RSVP streams where the items flanking Target 1 either had the same identity (repeats) or a different identity (non-repeats). Repeated distractors reduced the attentional blink, but only if two conditions were met (1) the items flanking Target 1 were featurally identical and (2) the distractors were drawn from a different alphanumeric category to the targets (e.g. digits vs. letters). We interpret this reduced blink magnitude in the repeat trials as evidence that in RSVP streams distractor items that appear in close temporal proximity to Target 1 are inhibited and we propose that this inhibition occurs both at the level of alphanumeric features and abstract identities.     

Effects of age on searching for and enumerating targets that cannot be detected efficiently

We investigated the effects of old age on search, subitizing, and counting of difficult-to-find targets. In Experiment 1, young and older adults enumerated targets (Os) with and without distractors (Qs). Without distractors, the usual subitization-counting function occurred in both groups, with the same subitization span of 3.3 items. Subitization disappeared with distractors; older adults were slowed more overall by their presence but enumeration rates were not slowed by ageing either with or without distractors. In contrast, search rates for a single target (O among Qs) were twice as slow for older as for young adults. Experiment 2 tested and ruled out one account of age-equivalent serial enumeration based on the need to subvocalize numbers as items are enumerated. Alternative explanations based on the specific task differences between detecting and enumerating stimuli are discussed.     

Extracting thresholds from noisy psychophysical data

Psychophysical studies with infants or with patients often are unable to use pilot data, training, or large numbers of trials. To evaluate threshold estimates under these conditions, computer simulations of experiments with small numbers of trials were performed by using psychometric functions based on a model of two types of noise:stimulus-related noise (affecting slope) andextraneous noise (affecting upper asymptote). Threshold estimates were biased and imprecise when extraneous noise was high, as were the estimates of extraneous noise. Strategies were developed for rejecting data sets as too noisy for unbiased and precise threshold estimation; these strategies were most successful when extraneous noise was low for most of the data sets. An analysis of 1,026 data sets from visual function tests of infants and toddlers showed that extraneous noise is often considerable, that experimental paradigms can be developed that minimize extraneous noise, and that data analysis that does not consider the effects of extraneous noise may underestimate test-retest reliability and overestimate interocular differences.     

Visual search in typically developing toddlers and toddlers with Fragile X or Williams syndrome

Visual selective attention is the ability to attend to relevant visual information and ignore irrelevant stimuli. Little is known about its typical and atypical development in early childhood Experiment 1 investigates typically developing toddlers' visual search for multiple targets on a touch-screen. Time to hit a target, distance between successively touched items, accuracy and error types revealed changes in 2- and 3-year-olds' vulnerability to manipulations of the search display. Experiment 2 examined search performance by toddlers with Fragile X syndrome (FXS) or Williams syndrome (WS). Both of these groups produced equivalent mean time and distance per touch as typically developing toddlers matched by chronological or mental age; but both produced a larger number of errors. Toddlers with WS confused distractors with targets more than the other groups; while toddlers with FXS perseverated on previously found targets. These findings provide information on how visual search typically develops in toddlers, and reveal distinct search deficits for atypically developing toddlers.     

身份交换对多身份追踪表现的影响

本研究探讨了身份交换对多身份追踪表现的影响。实验1和实验2分别考察了全部报告法和部分报告法下身份交换对多身份追踪表现的具体影响。结果均发现, 身份交换对身份−位置绑定干扰程度越大, 位置追踪和身份识别容量也均越低, 但位置容量始终高于身份容量, 并且这些特性在不同追踪负荷上相同。此外, 部分报告法比全部报告法更具有容量测量优势。实验3则进一步从听觉通道上控制了语音复述对当前任务的干扰, 所得结果仍支持实验1和实验2。这表明, 身份交换对多身份追踪的干扰机制是身份−位置绑定机制受到损害, 而非语音复述的作用。     

Aging and enumeration: a selective deficit for the subitization of targets among distractors

The term subitization has been used to refer to the fast and accurate enumeration of up to about 4 items. Beyond 4 items, enumeration becomes more serial and less accurate, with each additional item adding to the total enumeration time. The effects of aging on visual enumeration of targets (Os) were assessed with and without the presence of distractors (Xs). Young participants (n = 30; 18-27 years) showed the usual subitization-counting enumeration function, both with and without the presence of distractors. In contrast, for older participants (n = 35; 65-79 years), evidence for subitization was found only when distractors were absent. This occurred even though they could detect an individual target among distractors in parallel across the field. The results are discussed in relation to recent theories of visual selection and enumeration.     

Parallel pattern processing and visual agnosia.

A series of visual search experiments are reported examining pattern processing in a visual agnosic patient. We examined search for targets defined by: (I) the combination of their features relative to homogeneous distractors; (2) the combination of their features relative to heterogeneous distractors; and (3) a single feature difference relative to the distractors (their orientation). Normal subjects demonstrate evidence of spatially parallel search when combined-feature targets are detected against homogeneous distractors, and when targets are defined by a salient feature difference. There are non-linear effects of the number of distractors present, and absent responses can be as fast as present. In contrast, search times for combined-feature targets amongst heterogeneous distractors increase linearly with display size, with the slope for absent responses about twice that for present. The contrast between search for combined-feature targets amongst homogeneous and heterogeneous distractors can be attributed to the effects of grouping between distractors and between distractors and targets (Duncan & Humphreys, 1989, 1992; Humphreys & Muller, in press). Grouping between homogeneous distractors facilitates search. An agnosic patient, HJA, showed normal search functions for single-feature targets and for combined-feature targets amongst heterogeneous distractors. However, he was impaired at search for combined-feature targets amongst homogeneous distractors. This suggests that HJA is selectively impaired at grouping conjunctions of form features. The relations between HJA's agnosia and his problem in the parallel grouping of form conjunctions are discussed, as are the implications of the work for understanding normal vision.     

Concurrent working memory load can facilitate selective attention: evidence for specialized load

Load theory predicts that concurrent working memory load impairs selective attention and increases distractor interference (N. Lavie, A. Hirst, J. W. de Fockert, & E. Viding). Here, the authors present new evidence that the type of concurrent working memory load determines whether load impairs selective attention or not. Working memory load was paired with a same/different matching task that required focusing on targets while ignoring distractors. When working memory items shared the same limited-capacity processing mechanisms with targets in the matching task, distractor interference increased. However, when working memory items shared processing with distractors in the matching task, distractor interference decreased, facilitating target selection. A specialized load account is proposed to describe the dissociable effects of working memory load on selective processing depending on whether the load overlaps with targets or with distractors.     

The effects of distractors in multiple object tracking are modulated by the similarity of distractor and target features

Is the effect of distractors in multiple object tracking dependent on the distractors sharing the features of the targets? In experiment 1, observers tracked five targets among five distractors that were identical to the targets and a number of additional distractors that were either identical to or featurally distinct from the targets. Results showed that distractors that are distinct from the targets in shape or color, or are stationary, impair tracking less than distractors that are identical to the targets. However, tracking performance declined as the number of distractors increased, even for featurally distinct distractors. Experiment 2 showed that distractors that differ from the targets on two features impair tracking less than distractors that differ from the targets on only one feature, but only when target tracking load is low. These results indicate that shape, color, and motion information about distractors can be used to distinguish them from targets during tracking, although even distractors with a different feature from the targets produce some interference with tracking. These findings suggest that the effect of distractors on tracking is dependent on top-down settings for target features.     

Memory as discrimination: What distraction reveals

Recalling information involves the process of discriminating between relevant and irrelevant information stored in memory. Not infrequently, the relevant information needs to be selected from among a series of related possibilities. This is likely to be particularly problematic when the irrelevant possibilities not only are temporally or contextually appropriate, but also overlap semantically with the target or targets. Here, we investigate the extent to which purely perceptual features that discriminate between irrelevant and target material can be used to overcome the negative impact of contextual and semantic relatedness. Adopting a distraction paradigm, it is demonstrated that when distractors are interleaved with targets presented either visually (Experiment 1) or auditorily (Experiment 2), a within-modality semantic distraction effect occurs; semantically related distractors impact upon recall more than do unrelated distractors. In the semantically related condition, the number of intrusions in recall is reduced, while the number of correctly recalled targets is simultaneously increased by the presence of perceptual cues to relevance (color features in Experiment 1 or speaker’s gender in Experiment 2). However, as is demonstrated in Experiment 3, even presenting semantically related distractors in a language and a sensory modality (spoken Welsh) distinct from that of the targets (visual English) is insufficient to eliminate false recalls completely or to restore correct recall to levels seen with unrelated distractors . Together, the study shows how semantic and nonsemantic discriminability shape patterns of both erroneous and correct recall.     

Attentional enhancement during multiple-object tracking

What is the role of attention in multiple-object tracking? Does attention enhance target representations, suppress distractor representations, or both? It is difficult to ask this question in a purely behavioral paradigm without altering the very attentional allocation one is trying to measure. In the present study, we used event-related potentials to examine the early visual evoked responses to task-irrelevant probes without requiring an additional detection task. Subjects tracked two targets among four moving distractors and four stationary distractors. Brief probes were flashed on targets, moving distractors, stationary distractors, or empty space. We obtained a significant enhancement of the visually evoked P1 and N1 components (～100–150 msec) for probes on targets, relative to distractors. Furthermore, good trackers showed larger differences between target and distractor probes than did poor trackers. These results provide evidence of early attentional enhancement of tracked target items and also provide a novel approach to measuring attentional allocation during tracking.     

Incidental and intentional visual memory: What memories are and are not affected by encoding tasks?

Prior research into the impact of encoding tasks on visual memory (Castelhano & Henderson, 2005) indicated that incidental and intentional encoding tasks led to similar memory performance. The current study investigated whether different encoding tasks impacted visual memories equally for all types of objects in a conjunction search (e.g., targets, colour distractors, object category distractors, or distractors unrelated to the target). In sequences of pictures, participants searched for prespecified targets (e.g., green apple; Experiment 1), memorized all objects (Experiment 2), searched for specified targets while memorizing all objects (Experiment 3), searched for postidentified targets (Experiment 4), or memorized all objects with one object prespecified (Experiment 5). Encoding task significantly improved visual memory for targets and led to worse memory for unrelated distractors, but did not influence visual memory of distractors that were related to the target's colour or object category. The differential influence of encoding task indicates that the relative importance of the object both positively and negatively influences the memory retained.     

The affective consequences of visual attention in preview search

Comparisons of emotional evaluations of abstract stimuli just seen in a two-object visual search task show that prior distractors are devalued, as compared with prior targets or novel items, perhaps as a consequence of persistent attentional inhibition (Raymond, Fenske, & Tavassoli, 2003). To further explore such attention-emotion effects, we measured search response time in a preview search task and emotional evaluations of colorful, complex images just seen therein. On preview trials, the distractors appeared 1,000 msec before the remaining items. On no-preview trials, all the items were presented simultaneously. A single distractor was then rated for its emotional tone. Previewed distractors were consistently devalued, as compared with nonpreviewed distractors, despite longer exposure and being associated with an easier task. This effect was observed only in the participants demonstrating improved search efficiency with preview, but not in others, indicating that the attentional mechanisms underlying the preview benefit have persistent affective consequences in visual search.     

Some primitive mechanisms of spatial attention

Our approach to studying the architecture of mind has been to look for certain extremely simple mechanisms which we have good reason to suspect must exist, and to confirm these empirically. We have been concerned primarily with certain low-level mechanisms in vision which allow the visual system to simultaneously index items at multiple spatial locations, and have developed a provisional model (called the FINST model) of these mechanisms. Among the studies we have carried out to support these ideas are ones showing that subjects can track multiple independent moving targets in a field of identical distractors, and that their ability to track these targets and detect changes occuring on them does not generalize to non-targets or to items lying inside the convex polygon that they form (so that a zoom lens of attention does not fit the data). We have used a visual search paradigm to show that (serial or parallel) search can be confined to a subset of indexed items and the layout of these items is of little importance. We have also carried out a large number of studies on the phenomenon known as subitizing and have shown that subitizing occurs only when items can be preattentively individuated and in those cases location precuing has little effect, compared with when counting occurs, which suggests that subitizing may be carried out by counting active indexes rather than items in the visual field. And finally we have run studies showing that a certain motion effect which is sensitive to attention can occur at multiple precued loci. We believe that taken as a whole the evidence is most parsimoniously accounted for in terms of the hypothesis that there is an early preattentive stage in vision where a small number of salient items in the visual field are indexed and thereby made readily accessible for a variety of visual tasks.     

Interference between maintenance and processing in working memory: the effect of item-distractor similarity in complex span

Four experiments examined the effect of phonological similarity between items and distractors on complex span performance. Item-distractor similarity benefited serial recall when distractors followed the items they were similar to, but not when distractors preceded the items they were similar to. These findings are predicted by C-SOB (contextual serial order in a box), a computational model of complex span. The model assumes that distractors are involuntarily encoded into memory, being associated to the preceding item's list position. Distractors interfere with items by superposition of distributed representations that are associated to the same position. Superposition distorts item memory; this distortion is less severe when the distractor is similar to the item. Further support for the assumption that distractors are encoded at the position of the preceding item comes from the finding that intrusions of distractors at recall tended to come from the position of the target item. In addition, intruding distractors tend to replace items to which they are similar, showing that lack of distinctiveness also contributes to interference.