Intertrial effects of same-different judgements

Specific intertrial effects (repetition effects) and general intertrial effects (refractoriness or persisting attention to the preceding trial) were studied with the same-different judgment task, which dissociates the effects of response repetition and stimulus repetition. Response repetition alone did not facilitate performance. Stimulus repetition did aid performance, but mainly when accompanied by response repetition. Subjects tended to avoid the normal comparison process by using the (invalid!) “bypass rule” (Fletcher and Rabbitt, 1978): repeat the response if the stimulus or some aspect thereof (letter contents, size, position) is repeated from the preceding trial, otherwise change the response. As to general effects, partial refractoriness was evident at response execution, but not at earlier processing stages. Mean RT increased, but errors decreased, as the response-stimulus interval (RSI) between trials decreased. Presenting a new letter pair immediately after the preceding response produced a delay, but subjects used the waiting time, while the response system recovered or was redirected to the present trial, to improve the accuracy of their decision.     

刺激结构对视觉定位的影响

本实验采用多点定位作业,结合部分报告法,研究视觉刺激的整体结构对定位成绩的影响。所呈现的刺激为1、2、3或4个颜色点。其中2、3、4点刺激分别是直线、正三角形和正方形。结果发现,当呈现时间较长时,1点和2、3、4点的定位误差无显著差异。但是1点的定位反应时却显著少于2、3、4点。这提示出现视觉定位的结构效应。而当呈现时间较短时,却没有这种结构效应。实验还发现,这种结构效应并不因刺激结构的不同而有区别。     

Two bs or not two Bs? A signal detection theory analysis of repetition blindness in a counting task

Stimulus repetition usually benefits performance. A notable exception is repetition blindness (RB), in which subjects fail to report a repeated stimulus in a rapid serial visual presentation. Theories differ in attributing RB to either perceptual encoding or memory retrieval and to impaired discrimination versus response bias. In the present study, subjects judged whether one or two letters were imbedded in sequences of digits. Unlike previous studies, false guesses of two unrepeated letters were distinguished from false guesses of two repeated letters. When repeated- and unrepeated-letter trials were randomly intermixed (Experiment 1), RB was entirely attributable to response bias. However, when they were separately blocked (Experiments 2 and 3), RB was manifested in discriminability (d'). The results support perceptual-encoding accounts of RB but indicate that effects on discriminability depend on subjects' processing strategies.     

Short-term retention of visually presented stimuli: some evidence of visual encoding.

Subjects saw two visual stimuli on each trial, separated by an interval ranging from 0 to 8 sec. Each stimulus was composed of a subset of the dots of a 7 × 5 dot matrix. In particular, it was a composite of two patterns, one of which formed a capital English letter and the other of which was an arrangement formed by 8 randomly selected dots. The task was to decide as quickly as possible whether the two stimuli contained the same letter. Under one condition (correlated noise) the same noise pattern was used with both letters; thus the decision as to whether the letters were the same could be based on a test of congruence of the two stimuli, noise and all. Under another condition (uncorrelated noise) the noise patterns differed, assuring that the composite patterns differed, and thus precluding congruence testing as an adequate way to determine whether the two letters were the same. Performance was better (RTs and error rates were smaller) with the correlated noise than with the uncorrelated noise. The result was taken as evidence that visual information was retained in memory, and used to advantage, when the situation clearly warranted the direct comparison of visual patterns.     

Effects of laterality and visual angle on time judgments: a phenomenological investigation of time durations

20 students from an undergraduate class participated in an experiment designed to study the effects of laterality and visual angle on time judgments. Using a standard two-field tachistoscope , subjects were exposed to two experimental conditions, (1) stimulus cards with a single red or blue dot in the center and several dots clustered on both sides near the center and equidistant from it (visual angle of .6 degrees) and (2) stimulus cards with a single red or blue dot in the center and several dots clustered on both sides away from the center on the edge of the card (visual angle of 2.6 degrees). Five cards containing a single red or blue dot were used to control for response bias. The subjects were asked to indicate whether they saw dots in the left, right, or both fields, and whether they perceived a time duration between fields. No difference in time duration existed, however, as all cards were exposed to both fields for equal durations. The predictions that the judged duration of dot patterns would be more accurate favoring the left visual-field and more accurate where the distance between the point of fixation and stimulus was larger were supported.     

Processing of repeated letters in search and matching tasks

Several published experiments have used a variant of the matching or “same”-“different” paradigm in which the subject indicates whether or not all of the items in a visual array are the same. Contrary to the results of most paradigms in which subjects process multiple items, reaction time (RT) in this matching task is independent of the number of items in the display (N). One possible explanation of this independence holds that subjects respond to some overall property of the display, such as its general symmetry, and not to the individual items. I tested this hypothesis with a visual search task in which subjects searched a circular display of N=2, 4, or 6 letters for a specified target letter under three stimulus conditions. In the varied condition, the nontarget letters were all different from each other. In the repeated condition, the nontargets were repetitions of the same letter, but a single discrepant letter was always present in the display. The uniform condition also used repeated nontargets, but the negative (target-absent) displays contained N repetitions of a single nontarget item. I found that RT increased at a rate of 27 msec/item for the varied condition, but at only 13 and 8 msec/item in the repeated and uniform conditions, respectively. The slopes in the latter conditions were significantly lower than the slope for the varied condition, and they also differed significantly from each other. Hence, there was some advantage attributable to properties of the overall patterns associated with positive and negative responses, suggesting that at least some responses were based on these properties. There was a much larger advantage, however, attributable to the use of repeated nontargets, regardless of whether the overall patterns differed. This latter observation implies that the flat RT functions observed in matching studies must be interpreted primarily in terms of responses to individual items rather than to the pattern as a whole.     

Sequential priming is not constrained by the shape of long-term learning curves

When multiple stimulus-to-response (S-R) mappings are randomly intermixed and repeated in a block of trials, immediate repetitions of an aspect of a stimulus and/or a response can facilitate stimulus detection, classification, and/or response selection--known as sequential priming. In addition to these short-term effects, response times (RT) for almost any task diminish with extended practice, improvements can occur over many days, and RT learning curves typically assume exponential or power functions. We investigated whether short-term sequential priming and long-term practice modulate RT through a common mechanism, using a variant of the additive factors method. We tracked how various priming effects, presumably affecting different processing stages (e.g, stimulus selection, stimulus identification/classification, and S-R mapping), varied over training sessions as RT diminished. All the priming effects either were not reduced or reduced approximately linearly at rates much slower than those predicted by the shapes of the coresponding RT learning curves. The overall results suggest that short term sequential priming and long-term practice modulate RT through relatively separate mechanisms, even though they appear to affect a common set of behaviorally defined processing stages.     

Rethinking volitional control over task choice in multitask environments: Use of a stimulus set selection strategy in voluntary task switching

Under conditions of volitional control in multitask environments, subjects may engage in a variety of strategies to guide task selection. The current research examines whether subjects may sometimes use a top-down control strategy of selecting a task-irrelevant stimulus dimension, such as location, to guide task selection. We term this approach a stimulus set selection strategy. Using a voluntary task switching procedure, subjects voluntarily switched between categorizing letter and number stimuli that appeared in two, four, or eight possible target locations. Effects of stimulus availability, manipulated by varying the stimulus onset asynchrony between the two target stimuli, and location repetition were analysed to assess the use of a stimulus set selection strategy. Considered across position condition, Experiment 1 showed effects of both stimulus availability and location repetition on task choice suggesting that only in the 2-position condition, where selection based on location always results in a target at the selected location, subjects may have been using a stimulus set selection strategy on some trials. Experiment 2 replicated and extended these findings in a visually more cluttered environment. These results indicate that, contrary to current models of task selection in voluntary task switching, the top-down control of task selection may occur in the absence of the formation of an intention to perform a particular task.     

Response conflict determines sequential effects in serial response time tasks with short response-stimulus intervals

In serial choice reaction time (RT) tasks, performance in each trial critically depends on the sequence of preceding events. In this study, the authors specifically examined the mechanism underlying RT sequence effects at short response-stimulus intervals (RSIs), in which performance is impaired in the current trial N if events alternate rather than repeat from trial N-2 to trial N-1. Different accounts of this RT pattern in terms of perceptual noise, response-selection monitoring, and response conflict were tested in 4 experiments. Second-order RT costs were caused by the response sequence rather than the stimulus sequence. Manipulation of stimulus contrast, stimulus classification difficulty, and set-level compatibility did not modulate the response-related second-order RT effect, whereas this effect increased when spatially incompatible responses were demanded. These findings support a response conflict account of higher order sequential effects in short-RSI situations.     

Processing redundant signals: coactivation, divided attention, or what?

The evidence for and against a redundancy gain in reaction time (RT) when the target is repeated in the visual display is reviewed. We consider the relevance of redundancy gains under these circumstances to the question of whether attention can be simultaneously directed to separate locations in the visual field. In the present experiments, two capital letters were the target stimuli in a two-alternative forced-choice RT paradigm. In addition to the usual conditions of single-target trials, trials on which the target is repeated in the display, and trials on which the target occurs with a noise letter, we introduced the innovation of a condition in which both targets occur in the display. In our two experiments, RT was fastest with single-target displays and slowest with displays containing a target and a noise letter. There was no significant difference in RT to displays in which the target was repeated and displays in which both targets were presented. Both conditions showed a redundancy gain when compared with displays containing a target and a noise letter. The lack of response competition in the both-targets condition and the overall pattern of the results were well explained by a unitary attentional focus that serially processed the letters in the display. Analyses of minima and maxima RTs were consistent with this interpretation.     

Detection of visual patterns disturbed by noise: An exploratory study

An introductory study of the perception of stochastically specified events is reported. The initial problem was to determine whether the perceiver can split visual input data of this kind into random and determined components. The inability of subjects to do so with the stimulus material used (a filmlike sequence of dot patterns), led to the more general question of how subjects code this kind of visual material. To meet the difficulty of defining the subjects' responses, two experiments were designed. In both, patterns were presented as a rapid sequence of dots on a screen. The patterns were more or less disturbed by “noise,” i.e. the dots did not appear exactly at their proper places. In the first experiment the response was a rating on a semantic scale, in the second an identification from among a set of alternative patterns. The results of these experiments give some insight in the coding systems adopted by the subjects. First, noise appears to be detrimental to pattern recognition, especially to patterns with little spread. Second, this shows connections with the factors obtained from analysis of the semantic ratings, e.g. easily disturbed patterns show a large drop in the semantic regularity factor, when only a little noise is added.     

A partial repetition effect in choice reaction time for multidimensional stimuli

Bertelson (1963), and others more recently, have observed that when the same stimulus is presented consecutively the reaction time (RT) to the second presentation is faster than the RT to the first presentation. In Experiments 1 and 2, two-dimensional stimuli are used in a discrete four-choice RT task where the stimuli can either be completely repeated, partially repeated, or completely different. In Experiment 3, three-dimensional stimuli were used in a discrete eight-choice RT task where the stimuli can either be completely repeated, partially respeated with respect to two dimensions, partially repeated with respect to one dimension, or completely different. The partial repetition of multidimensional stimuli showed a significant facilitation effect on RT with all sets of stimuli used in the present experiments. This result is discussed in respect to the various possible loci of the repetition effect.     

Judgments of perceptual groups: reliability and sensitivity to stimulus transformation

The reliability of subjects' judgments of the groups present in dot patterns and the sensitivity of those judgments to stimulus transformation were assessed. The subjects indicated the groups that they saw within random dot patterns, and each judgment was compared with those of other subjects and with their own judgments for related presentations. Within subjects, each pattern appeared in an initial presentation, an identical repetition, and a transformed state (a rotation or a change in scale). Within-subjects judgments were more reliable than between-subjects judgments. An interpretation of within-subjects results was made in relation to predictions made by a formal algorithm of grouping by proximity (the CODE algorithm), which assumes that grouping by proximity is invariant over transformations such as rotations or changes in scale. A slight cost to transforming the patterns was found. The implications for CODE and for using grouping judgments as data are discussed.     

A unilateral field advantage for detecting repeated elements

Previous studies have shown that letter repetitions are detected more rapidly when presented bilaterally (one letter in each visual field) than when presented unilaterally (both in the same field) when subjects have to report matches independently of case or font (e.g., Aa). This pattern of results is referred to as a bilateral field advantage. Here, we present evidence of an opposite pattern of results for detecting repeated items when they are physically identical. In our repetition detection paradigm, subjects indicated whether there was a repetition of any two of four presented items, one in each quadrant of the visual field. Stimulus classes tested included letters, color, size, orientation, and motion paths. The subjects were significantly faster at detecting unilateral versus bilateral repetitions for four out of the five stimuli classes tested, with a trend in the same direction for the fifth. This unilateral field advantage suggests that low-level processes group physically identical items more efficiently within hemifields than across.     

Judgments of perceptual groups: Reliability and sensitivity to stimulus transformation

The reliability of subjects’ judgments of the groups present in dot patterns and the sensitivity of those judgments to stimulus transformation were assessed. The subjects indicated the groups that they saw within random dot patterns, and each judgment was compared with those of other subjects and with their own judgments for related presentations. Within subjects, each pattern appeared in an initial presentation, an identical repetition, and a transformed state (a rotation or a change in scale). Witfiin-subjects judgments were more reliable than between-subjects judgments. An interpretation of within-subjects results was made in relation to predictions made by a formal algorithm of grouping by proximity (the CODE algorithm), which assumes that grouping by proximity is invariant over transformations such as rotations or changes in scale. A slight cost to transforming the patterns was found. The implications for CODE and for using grouping judgments as data are discussed.     

Recognition of rotated letters: extracting invariance across successive and simultaneous stimuli.

Response time (RT) for identifying single letters is usually indifferent to disorientation, but in Experiment 1 RT increased with the angular deviation from that of the preceding letter (ADP). This occurs only when the same letter is repeated, which suggests a process of backward alignment. RT again increased with ADP when the same letter was repeated in the same format (normal or mirror-reflected: Experiment 2). These findings were replicated for a same-different task by using 2 simultaneously presented letters (Experiment 3). Experiments 4 and 5 focused on stimuli that are related by a rotation in depth and suggested that transformation in the depth plane may facilitate judgments of sameness and that backward alignment can occur for different views of the same three-dimensional shape. The results suggest the operation of a pattern-recognition mechanism that relies on the extraction of invariance over temporally or spatially contiguous events.     

Types and tokens in visual letter perception

Five experiments demonstrate that in briefly presented displays, subjects have difficulty distinguishing repeated instances of a letter or digit (multiple tokens of the same type). When subjects were asked to estimate the numerosity of a display, reports were lower for displays containing repeated letters, for example, DDDD, than for displays containing distinct letters, for example, NRVT. This homogeneity effect depends on the common visual form of adjacent letters. A distinct homogeneity effect, one that depends on the repetition of abstract letter identities, was also found: When subjects were asked to report the number of As and Es in a display, performance was poorer on displays containing two instances of a target letter, one appearing in uppercase and the other in lowercase, than on displays containing one of each target letter. This effect must be due to the repetition of identities, because visual form is not repeated in these mixed-case displays. Further experiments showed that this effect was not influenced by the context surrounding the target letters, and that it can be tied to limitations in attentional processing. The results are interpreted in terms of a model in which parallel encoding processes are capable of automatically analyzing information from several regions of the visual field simultaneously, but fail to accurately encode location information. The resulting representation is thus insufficient to distinguish one token from another because two tokens of a given type differ only in location. However, with serial attentional processing multiple tokens can be kept distinct, pointing to yet another limit on the ability to process visual information in parallel.     

前额叶神经振荡活动反映了稳固的刺激冲突和反应冲突

为考察典型Flanker任务中练习对刺激冲突和反应冲突的影响,本研究采用练习范式记录被试完成2:1字母Flanker任务时的行为和脑电数据。行为结果发现,练习对这两类冲突无显著影响。神经震荡能量结果发现,前额叶theta能量随练习而显著减弱,这暗示刺激-反应之间的联结因练习而提升;前额叶alpha能量差异不随练习而变化,这可能反映了Flanker任务中稳定的刺激冲突和反应冲突加工机制。因此,本研究揭示了典型Flanker任务中刺激冲突和反应冲突的稳定特征。     

Effect of stimulus repetition on positive and negative identity priming

Most negative-priming experiments have used a limited number of stimuli that are repeated many times throughout the experiment. We report five experiments that examine in greater detail the role of stimulus repetition in negative priming. Subjects were presented with displays consisting of two or more words, and were required to name the word printed in red. On attended repetition (AR) trials, the target word was the same as the target word on the preceding trial. On ignored repetition (IR) trials, the target word was the same as the distractor word on the preceding trial. Experiments 1 and 2 used novel words, and obtained positive priming on AR trials, but no negative priming on IR trials. Experiments 3 and 4 used repeated words, and obtained negative priming on IR trials, but no positive priming on AR trials. In Experiment 5, both novel and repeated words were intermixed, and negative priming was observed for repeated, but not novel, IR conditions, whereas positive priming was observed for novel, but not repeated, AR conditions. Together, Experiments 1–5 demonstrate that positive and negative identity priming are modulated by stimulus repetition and are stimulus specific.     

Does symmetry structure facilitate the depth separation between stereoscopically overlapped dot planes?

In the present study, we dealt with the problem of whether a symmetrical structure can influence the discrimination of the depth separation of overlapped dot planes. We investigated this problem with the use of both direct and indirect methods. In the direct method, we presented three or two overlapped dot planes consisting of symmetrical or random dots. The subjects were required to discriminate three overlapped from two overlapped planes. In the indirect method, the subjects were required to discriminate the depth positions of a target dot (or a pair of dots) that disappeared during stimulus presentation. Our results, obtained in three experiments, showed that the discrimination performance improved and reached a perfect level in the direct method and a modest plateau level in the indirect method with increasing relative disparity between the two outer planes, irrespective of whether the dot pattern had a symmetrical structure or not. These results suggest that a detection process for symmetry structure on a two-dimensional plane in three-dimensional space will not have a direct or an indirect connection (e.g., via a feedback loop) to a process involved in the depth separation.