Memory for attended and unattended visual stimuli

Subjects were presented with lists of 'compound letters,' letters whose overall shapes were described by repeated use of replicates of other, smaller letters. In Experiment 1 subjects were asked to attend to either the overall letter or the smaller, constituent letter. At the end of list presentation, recall of all letters was required, but a postlist cue determined whether the attended or unattended letters were to be reported first. The results for four-item lists accorded with those of Martin (1978, 1980): order of report had a larger effect upon retention of attended letters than upon retention of unattended letters. The findings for three-item lists did not agree with Martin, however: first, the interaction of attention and order was weak; second, sharp recency for unattended letters was not found.

Experiment 2 required that subjects recall either in temporal pairs or by letter size. The results strongly suggest that the present paradigm does not constitute an analogue to dichotic listening. In particular, there is little evidence for a role for sensory retention of compound letters at time of recall.     

Can the spotlight of attention be shaped like a doughnut? Evidence from steady-state visual evoked potentials

Visual attention enables observers to extract and process high-priority information in the visual field. Controversy remains as to whether or not observers can ignore information that falls within the spatial beam of attention. We used an objective physiological measure, the steady-state visual evoked potential (SSVEP), to investigate this question. A stream of flickering small, uppercase letters was embedded in the center of a stream of large, uppercase letters. A unitary beam would result in no difference of the SSVEP amplitude elicited by the small letter stream when it was attended versus ignored (i.e., when subjects attended the large letter stream). Contrary to this prediction, SSVEP amplitude increased by almost 100% when the small letter stream was attended compared with when it was ignored. The results support the notion that the attentional spotlight can be formed like a doughnut, processing central information differentially depending on whether it is attended or ignored.     

Speed of letter cancellation on the basis of visual and name identity in young children

Second-, fourth-, and sixth-grade children were tested on a visual search task where letter matching was based on the visual or name characteristics of letters. Visual match lists were searched faster than name match lists by all three grades. In the name match lists there was an increase in speed as a function of trials whereas in the visual match lists there was no increase. The name-physical match difference did not change as a function of age.     

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.     

Repetition blindness and illusory conjunctions: errors in binding visual types with visual tokens.

Repetition blindness (Kanwisher, 1986, 1987) has been defined as the failure to detect or recall repetitions of words presented in rapid serial visual presentation (RSVP). The experiments presented here suggest that repetition blindness (RB) is a more general visual phenomenon, and examine its relationship to feature integration theory (Treisman & Gelade, 1980). Experiment 1 shows RB for letters distributed through space, time, or both. Experiment 2 demonstrates RB for repeated colors in RSVP lists. In Experiments 3 and 4, RB was found for repeated letters and colors in spatial arrays. Experiment 5 provides evidence that the mental representations of discrete objects (called "visual tokens" here) that are necessary to detect visual repetitions (Kanwisher, 1987) are the same as the "object files" (Kahneman & Treisman, 1984) in which visual features are conjoined. In Experiment 6, repetition blindness for the second occurrence of a repeated letter resulted only when the first occurrence was attended to. The overall results suggest that a general dissociation between types and tokens in visual information processing can account for both repetition blindness and illusory conjunctions.     

Large auditory and small visual effects in the recall of consonant letters

Eighty-six adults serially recalled lists of visually presented consonant letters similar in auditory or visual features or dissimilar in both feature sets. There were significantly more errors at every auditory list position than at the corresponding visual and neutral list positions, which did not themselves differ. There was a positive correlation between the tendency toward phonetic coding and overall performance, with 75 subjects making more errors on the auditory list than either of the other lists. The eight subjects who made more errors on the visual list showed poor performance in the recall of all lists. Factors governing the perceivability of stimuli apparently do not continue to operate significantly in controlling their recallability, at least in the case of veridical visual input.     

Transfer of stimulus differentiation and perceptual selection rules

Three experiments examined the conditions under which transfer of stimulus differentiation occurs. Two experiments involved transfer in paired associate lists having identical stimuli and re-paired response terms compared with lists having different stimuli. In one experiment, transfer was determined for lists of three-word stimuli in which various elements were shared among the stimuli. The pattern of redundancy was such that the spatial position of a discriminative element was either consistent or not consistent in different items, or there was no discriminative element. Transfer of differentiation was obtained only when position was constant. In the second experiment, stimuli were single words and were either unrelated, rhymed, or were instances of common concepts. No evidence of transfer of differentiation was obtained with either rhymes or concepts. In the third experiment, subjects learned pairs in which the stimuli were single letters; then subjects transferred to a list in which either rhyming or unrelated stimuli began with the same letters. Transfer was not differential.     

Absence of a cross-modal “suffix effect” in short-term memory

Three experiments are reported involving the presentation of lists of either letters or digits for immediate serial recall. The main variable was the presence or absence of a suffix-prefix, an item (tick or cross) occurring at the end of the list which had to be copied before recall of the stimulus list. With auditory stimuli and an auditory suffix-prefix there was a large and selective increase in the number of errors on the last few serial positions—the typical “suffix effect”. The suffix effect was not found with auditory stimuli and a visual suffix-prefix nor with a visual stimulus and an auditory suffix-prefix. These results are interpreted as supporting a model for short-term memory proposed by Crowder and Morton (1969) in which it is suggested that with serial recall information concerning the final items following auditory presentation has a different, precategorical, origin from that concerning other items.     

New evidence for the perceptual precedence of global information

Two experiments are reported investigating the order in which global and local information of visual forms is processed. Subjects were presented with compound stimuli and were asked to identify the local level, always consisting of small letters. At the global level, the stimuli could be either large letters, consistent or inconsistent with the local level, or meaningless patterns derived from the large letters by modifying the spatial relations among segments. Results showed that inconsistent stimuli were responded to more slowly than both consistent stimuli and meaningless patterns, which did not differ from each other. This was true both when letters and patterns were presented intermixed, as in experiment 1 or separately, as in experiment 2. The pattern obtained accords well with predictions derived from the perceptual precedence hypothesis which states that global information becomes available at a faster rate than local information. No support for the alternative, post-perceptual, hypothesis was found.     

Vocalization-at-presentation and immediate recall, with varying presentation-rates

An experiment is reported in which the subject read visually presented lists with four different degrees of vocalization; immediately after reading each list he was required to reproduce it either aloud or in writing. Each list consisted of eight consonants and presentation rates were varied between I and 4 letters per sec. For any given series of lists, the subject was asked either to read the letters silently, or to mouth them silently, or to whisper them, or to say them aloud while reading.

At the fastest presentation-rate immediate recall improved monotonically with the degree of vocalization during reading of the lists; at slower rates this generalization held less well, especially for the lower degrees of vocalization. Vocalization was most helpful at the highest presentation-rate.

The overall amount correctly recalled was better for more slowly presented lists and for written as opposed to spoken recall. Analysis of the errors suggested that acoustic confusions were affected by the conditions of presentation; and that serial order intrusions were independent of presentation-or recall-conditions. An apparent variation of transpositions with voicing-and-recall-method failed to reach statistical significance. Theoretical implications of the experiment are discussed, including reference to Broadbent's theory of short-term memory (1958).     

Feature similarity and feature bias in identification of visually presented letters

Reaction time IRT) to correct identification (ID) was measured for pairs of different letters presented on a memory drum. There were two types of lists. In Type I, visual and name similarity varied orthogonally at two levels. In Type II, one feature was constant at one level, while the other varied at two levels of similarity. For both types of lists, RT is a function of the feature that is more easily extracted from the stimulus. Relative vivaal and name modality biases were estimated, and name bias is relatively more salient than visual bias under these experimental conditions. Specific letters differ in the amount of feature processing required for correct ID and in the relative contribution of visual and name feature effects on this processing.     

Lorazepam,a Benzodiazepine,Induces Atypical Distractor Effects with Compound Stimuli: A Role for Line-ends in the Processing of Compound Letters

The present study was designed to dissociate the effect of a single dose of lorazepam (a benzodiazepine, GABA_A-agonist) on the processing of spatial frequency, visual integration, and attentional processes in healthy volunteers. The stimuli were composed of small letters spatially organized to form a large letter. The task was to decide which of two target letters was displayed, either as a small or the large letter. Effects of spatial frequency and attentional processing were explored by manipulating respectively the visual angle of the stimuli and the probability that the targetwould appear at the local or at the global level. The results showed no evidence of a lorazepam effect on spatial frequency or attentional processing, but there was an atypical distractor effect when the target was a large letter, related to the arrangement of line-ends. The results are discussed in relation to studies showing the involvement of GABA in the generation of neuronal responses to line-ends.     

Visual search through words and nonwords in horizontal and vertical orientations.

In a repeated measurement design, 18 college women searched for target letters in 18 lists of common words, rare words, and nonwords arranged either vertically or horizontally. The mean search time in seconds for three trials in each of six conditions was expected to be significantly slower for nonwords than for words and for vertical orientations than for horizontal orientations. More importantly, a significant interaction was predicted between direction of search and the type of list searched. Results confirmed earlier findings that the two main effects were significant; the significant interaction provided empirical evidence that consideration needs to be given to both intraword redundancy and direction of visual search.     

Moray vs. the rest: The effects of extended shadowing practice

The processing requirements of the shadowing response have led to criticisms of its use in selective attention experiments. The present experiment tested a single highly skilled shadower (N. Moray) using a task requiring the detection of digits embedded in dichotic lists of letters, with attention being directed to one list by use of the shadow technique. This subject was able to detect considerably more digits in both the attended and unattended messages than were groups of unskilled shadowers previously tested. Although performance to the unattended message was high, it remained below performance to the attended message.     

Shifting of attentional focus within and about a visual display

If several positions must be attended in a large visual display, does the efficiency of performance vary as a function of the display distance between these to-be-attended positions? Two previous experiments (Podgorny & Shepard, 1983; Shaw, 1978) gave conflicting answers. In the present experiments, eight-letter circular displays were briefly presented. On each trial one, two, or three positions of the display were cued or precued. The number of noncued display positions intervening between the cued locations varied from zero to three. The subjects' task was to rapidly discriminate between two target letters. Although reaction time was found to increase with increases in the number of cued locations, no significant or suggestive effects were found for the spacing or distance between the cued locations. The evidence strongly suggests that the subjects serially searched the cued locations, which further implies that attention can index locations in the visual field at a speed that is independent of the distance between these locations.     

Retention of attended and unattended auditorily and visually presented material

In the first of two experiments investigating focussed attention, sets of four pairs of digits were dichotically presented to subjects who were instructed to attend to digits arriving in either the left or the right ear. Following presentation, two different report orders were used: attended followed by unattended, and unattended followed by attended. It was found that unattended items did not suffer from being recalled second rather than first. The serial position curve for unattended items was U-shaped. These results were interpreted as evidence that unattended items are not retained in a limited-capacity auditory buffer with a fast rate of loss. The experiment was repeated using visually presented pairs of letters. A similar pattern of results was obtained, consistent with the hypothesis that unattended items are recalled from a store with a large capacity and a very slow rate of loss.     

The influence of acoustic similarity on serial recall of letter sequences

Acoustic similarity is known to impair short-term memory (STM) for letter sequences. The present series of experiments investigated the effects of acoustic similarity on long-term retention. In the first experiment, subjects were asked to learn one of two lists of 8 letters, the letters being either of high or low acoustic similarity. Lists were visually presented for three trials, with subjects responding after each trial. Then subjects participated in an immediate memory task for digits which lasted for 20 min. Finally, subjects tried to recall the list of letters they had learned previously. Lists having items of high acoustic similarity were more difficult to recall on the first trial, but were better recalled on the delayed retention test. In a second experiment, groups of subjects were again asked to learn one of two lists of 8 letters differing in acoustic similarity, using different orders of the letters used previously. The procedures were identical except that in two groups, a STM task for digits intervened between the presentation and test of the letters. This intervening task minimized the effects of STM and eliminated the differences in retention found previously. In a third experiment, better long-term retention for material having high acoustic similarity was also obtained when subjects used a backward recall procedure. In the last experiment 14 item lists were learned to a criterion of two correct trials, and retention was tested after each trial and at a delay of 20 min. and 23 hr. No effect of acoustic similarity was found and little retention loss occurred. These results suggest that reducing the STM component by introducing a STM control or by lengthening the list caused the effect of acoustic similarity to disappear.     

掩蔽刺激对目标识别加工的作用：来自fNIRS的证据

信息掩蔽刺激(如随机字母群)对字母视觉搜索的干扰大于能量掩蔽刺激(如将字母群像素随机化后的散点), 但相应的中枢机理还不清楚。本研究采用记录脑代谢激活模式的功能性近红外光学脑成像技术(fNIRS), 考察年轻成年被试分别在字母掩蔽、字母碎片掩蔽、像素掩蔽条件下判断上、下、左、右四个目标字母是否相同时的大脑皮层氧合血红蛋白浓度的变化。结果显示, 依字母、字母碎片、随机散点掩蔽条件顺序, 被试的搜索任务成绩显著递增, 而顶-枕皮层的激活范围与程度显著递减, 表明信息掩蔽较匹配的能量掩蔽对视觉搜索有更大的干扰作用, 并在初级和联合视觉皮层引发更大的激活。在字母碎片掩蔽条件下, 视觉初级皮层部分区域的激活水平与搜索行为绩效的相关显著, 而在字母掩蔽条件下, 视觉联合皮层部分区域的激活水平与搜索行为绩效的相关显著。这进一步说明信息掩蔽中的字母掩蔽和字母碎片掩蔽的掩蔽作用在大脑皮层上所造成的加工负载存在差异。     

Effects of irrelevant object structure on early attention deployment

Event-related potential (ERP) studies have suggested that Gestalt principles or grouping factors in a visual scene modulate attention deployment in early visual processing. The present study examined the effects of an extrinsic grouping factor, region commonality, on early ERP spatial attention. Effects of sex were also explored, since the processing of task-irrelvant objects may differ between the sexes. Twenty-four participants were required to discriminate one side of rapidly-presented bilateral letters, and attention effects were indexed by hemispheric lateralization accroding to attended visual fields. In results, an early P1 attention effect (70–110 ms) increased when the letters were surrounded by an object, compared to the control stimulus without a complete object, and this result was more prominent in women than in men. The present study demonstrates that visual object and sex differences play a novel role at very early cortical stages of processing in attention deployment to a task-irrelevant visual structure.     

Recognition vs recall of visually vs acoustically confusable letter matrices

In an attempt to separate auditory and visual components in short-term memory, five subjects were exposed to letter matrices composed of six visually confusable letters, six acoustically confusable letters, or a mixture of the two, under two response conditions: recognition and recall. A 50-msec stimulus presentation was followed by a variable dark interval of 1, 250, 1,000, or 3,000 msec. In the recall condition, the interval was followed by a buzzer which signaled the subject to recall, in any order, as many letters as possible. In the recognition condition, the variable interval was followed by a second letter matrix which was either identical to the first matrix or differed from is by one letter. Subjects responded either "same" or "different." The results support the notion that the auditory component plays a major role in recall, whereas the visual component dominates in recognition.