Context dependence in visual feature processing

Summary Dependence in visual feature processing was studied with two identification experiments using briefly exposed stimuli. The basic stimuli consisted of two orthogonal line segments which formed either one of the four angles of a square, and the subject had to identify the location of the horizontal and vertical line segment making up a stimulus. In the first experiment, the two orthogonal line segments were sometimes separated by a gap. In the second experiment, either a 45° diagonal or a 135° diagonal or both were added to the right angles. With the observed response frequencies two forms of independence in feature detection were tested. Feature detection is called state independent if the detection of a feature is independent of the detection of another feature. According to context independence the detection of a feature is independent of the orientation and location of other features in the stimulus. Feature detection was shown to be context dependent whereas the hypothesis of state independence was not rejected, and state independence was unrelated to the size of the gap between the two orthogonal line segments in the first experiment. It was argued that the context effects obtained (context dependence) had occurred early in processing during the automatic activation of representational units corresponding to features before controlled search, interpretation and decision processes became involved.     

How important is a prime's gestalt for subliminal priming?

Masked stimuli (primes) can affect the preparation of a motor response to subsequently presented target stimuli. Under some conditions, reactions to the main stimulus can be facilitated (straight priming) or inhibited (inverse priming) when preceded by a compatible prime (calling for the same response). In the majority of studies in which inverse priming was demonstrated arrows pointing left or right were used as prime and targets. There is, however, evidence that arrows are special overlearned stimuli which are processed in a favorable way. Here we report three experiments designated to test whether the "arrowness" of primes/targets is a sufficient condition for inverse priming. The results clearly show that although inverse priming appeared when non-arrow shapes were used, the magnitude of the priming effect was larger with arrows. The possible reasons for this effect are discussed.     

Effect of line orientation on various information-processing tasks

The effects of interstimulus and stimulus-specific factors on central (vs. peripheral) oblique effects were examined using classification, focusing, discrimination, and sequential same-different tasks. Classification results showed that grouping the vertical with the horizontal line and the two diagonal lines with each other facilitated performance. Discrimination results revealed that the two diagonal lines were more confusable with each other than were the members of any other stimulus pair. Focusing results indicated that the vertical and horizontal lines served as better focusing stimuli. A set of sequential same-different tasks, each using only two alternative stimuli, allowed for the examination of stimulus-specific factors in focusing; the effects of similarity relations between all stimuli in the total set were greatly reduced by the constrained context. The two diagonal lines were the most difficult to compare and proved to be the worst foci in these tasks as well. In conclusion, there are two factors operating in the central oblique effect: greater confusability between the two diagonal lines and more favorable stimulus-specific properties of vertical and horizontal lines.     

The object-detection effect: configuration enhances perception.

Line drawings used by Weisstein and Harris (1974) are seen as box-like three-dimensional figures if the lines are arranged properly. A flat two-dimensional pattern is seen when these same lines are disarranged. A target line contained within the three-dimensional figure is identified more readily than is the same line contained within a two-dimensional figure. This finding was extended in the present experiments: The three-dimensional stimulus was detected more quickly than the two-dimensional stimulus, under conditions of visual backward masking. Three-dimensional stimuli were also classified more quickly than two-dimensional stimuli. Just as with the face-detection effect and the word-detection effect, object detection can be affected by the form of the visual stimulus.     

The object-detection effect: Configuration enhances perception

Line drawings used by Weisstein and Harris (1974) are seen as box-like three-dimensional figures if the lines are arranged properly. A flat two-dimensional pattern is seen when these same lines are disarranged. A target line contained within the three-dimensional figure is identified more readily than is the same line contained within a two-dimensional figure. This finding was extended in the present experiments: The three-dimensional stimulus was detected more quickly than the two-dimensional stimulus, under conditions of visual backward masking. Three-dimensional stimuli were also classified more quickly than two-dimensional stimuli. Just as with the face-detection effect and the word-detection effect, object detection can be affected by the form of the visual stimulus.     

Response priming with apparent motion primes

Response priming refers to the finding that a prime stimulus preceding a target stimulus influences the response to the following target stimulus. Typically, responses are faster and more accurate if the prime calls for the same response as the target (i.e., compatible trials), as compared with the situation where primes and targets trigger different responses (i.e., incompatible trials). However, the effect depends on presentational and temporal parameters such as the stimulus onset asynchrony (SOA) of prime and target, or prime duration. Until now, the special role of moving stimuli was largely ignored. In the present research, experiments were conducted using clearly visible moving dots as primes and static arrows as targets. Essentially, with short SOAs up to 200 ms, participants responded faster to compatible targets. In contrast, with SOAs above 200 ms, participants responded faster to incompatible targets. The results were compared with response priming with static primes. Here, a different pattern of results emerged, with faster responses to compatible than incompatible targets at a long SOA of 300 ms. Overall, the experiments provide evidence for the existence of an inhibitory mechanism in action control when (distracting) motion stimuli are present. Results could be explained with slight changes to different accounts of negative response priming effects, as well as theories of attention.     

Determinants of the Bourdon effect

The Bourdon illusion is the apparent inward bending of straight, collinear edges in a solid figure consisting of two elongated triangles meeting at their apexes. This effect was investigated in five experiments. In the first and third experiments, it was shown that the apparent bending is greatest when the apical angles are about 12 deg and the axis of the figure is oriented at about 22 deg from the vertical. The second experiment was a control involving visual acuity for angular departures of two lines from collinearity and served as a basis of selection for subjects in Experiments 3, 4, and 5. Experiments 4 and 5 showed that the illusion occurs strongly in a solid (“filled in”) figure but is notably smaller in outline figures of the same size and shape. It tends to be negative in outline figures with boundaries formed by continuous and broken lines. The relationship between the Bourdon illusion and the “negative” Zöllner illusion is considered.     

Can subthreshold summation be observed with the Ehrenstein illusion?

Subthreshold summation between physical target lines and illusory contours induced by edges such as those produced in the Kanizsa illusion has been reported in previous studies. Here, we investigated the ability of line-induced illusory contours, using Ehrenstein figures, to produce similar subthreshold summation. In the first experiment, three stimulus conditions were presented. The target line was superimposed on the illusory contour of a four-arm Ehrenstein figure, or the target was presented between two dots (which replaced the arms of the Ehrenstein figure), or the target was presented on an otherwise blank screen (control). Detection of the target line was significantly worse when presented on the illusory contour (on the Ehrenstein figure) than when presented between two dots. This result was consistent for both curved and straight target lines, as well as for a 100 ms presentation duration and unlimited presentation duration. Performance was worst in the control condition. The results for the three stimulus conditions were replicated in a second experiment in which an eight-arm Ehrenstein figure was used to produce a stronger and less ambiguous illusory contour. In the third experiment, the target was either superimposed on the illusory contour, or was located across the central gap (illusory surface) of the Ehrenstein figure, collinear with two arms of the figure. As in the first two experiments, the target was either presented on the Ehrenstein figure, or between dots, or on a blank screen. Detection was better in the dot condition than in the Ehrenstein condition, regardless of whether the target was presented on the illusory contour or collinear with the arms of the Ehrenstein figure. These three experiments demonstrate the ability of reduced spatial uncertainty to facilitate the detection of a target line, but do not provide any evidence for subthreshold summation between a physical target line and the illusory contours produced by an Ehrenstein figure. The incongruence of these results with previous findings on Kanizsa figures is discussed.     

Arrow-elicited cueing effects at short intervals: Rapid attentional orienting or cue-target stimulus conflict?

The observation of cueing effects (faster responses for cued than uncued targets) rapidly following centrally-presented arrows has led to the suggestion that arrows trigger rapid automatic shifts of spatial attention. However, these effects have primarily been observed during easy target-detection tasks when both cue and target remain on the screen until the behavioral response. We manipulated stimulus duration and task difficulty in an attention-cueing experiment to explore non-attentional explanations for rapid cueing effects. Contrary to attention-based predictions, short-interval cueing effects were observed only for long-duration cue and target stimuli, occurred even when the cue and target were presented simultaneously, and were driven by slowing of the uncued-target responses, rather than any facilitation for cued targets. We propose that, under these long-duration, short-interval conditions, the processing of the cue and target interact more extensively in the brain, and that when the cue and target convey incongruent spatial information (i.e., on invalidly cued trials) it leads to conflict-related slowing of responses.     

时序知觉重复启动效应的作用机制

先前研究发现,时序判断任务在启动的靶刺激先出现时出现了重复启动效应的反转,这是以往的理论所不能单独解释的。通过两个实验对我们提出的双加工表征匹配调节假说加以实证检验,实验结果支持了该假说。因此,双加工表征匹配调节假说能较完整地综合解释时序知觉重复启动效应的作用机制     

Inhibition of return for the length of a line?

Inhibition of return is most often measured using an exogenous spatial cuing method. The experiments presented here follow up on a small number of studies that have examined whether a similar effect occurs for nonspatial stimulus attributes. In Experiments 1 and 2, the task was to identify a target line as either short or long. In this context, targets on valid trials were of the same length as that of a preceding cue, whereas targets on invalid trials were of a different length than that of a preceding cue. The results were similar to those in spatial orienting studies in that responses were slower for valid than for invalid targets only at stimulus onset asynchronies (SOAs) longer than 300 msec. In Experiment 3, the stimuli were the same but the task was to detect the onset of the target line. This task change resulted in slower responses for valid than for invalid targets at all SOAs. A similar result was observed in Experiment 4, in which validity was defined by color rather than line length, and the task was to identify the target color. The discussion centers on an opponent process approach to interpreting cuing effects, and consequent difficulties in distinguishing spatial and nonspatial cuing effects based on their time course.     

The effect of context on visual representational momentum

Effects of background context on representational momentum -were examined in six experiments. In each experiment, three orientations of a target rectangle undergoing implied rotation (i.e., the inducing stimuli) were presented, and subjects judged whether the orientation of a fourth rectangle (i.e., the probe) was the same as or different from that of the third inducing stimulus. Target rectangles were enclosed within a larger square frame context during induction (i.e., presentation of the inducing stimuli), judgment (i.e., presentation of the probe), or both induction and judgment. If context during induction moved in the same direction as the inducing stimuli or if context during judgment was rotated slightly forward from the orientation of the final inducing stimulus, representational momentum was increased. If context during induction moved in the direction opposite to the inducing stimuli or if context during judgment was rotated slightly backward from the orientation of the final inducing stimulus, representational momentum was decreased or reversed. If context was present during both induction and judgment, direction of representational momentum was biased toward the context at judgment Implications of context for accounts of representational momentum are discussed, and a tentative model is proposed.     

Flexibility of attention between stimulus dimensions

Three experiments examined the flexibility of attention to the color and location dimensions of visual stimuli. Displays typically consisted of two curved lines, one a target and the other a distractor. Subjects were precued to the location of the target, and they made a speeded response to that item’s direction of curvature. In Experiment 1, a color difference between the stimuli facilitated selective attention to targets. Experiment 2 demonstrated that this effect was not automatic. Although component color differences were necessary for selective attention, they were not sufficient unless they reliably specified the target. Furthermore, when color was informative but the target was in an unexpected color, performance was markedly impaired. A third experiment, using a response-deadline technique, showed that stimulus color was resolved before stimulus location and that attention can be exclusive to the color dimension. The results were interpreted in terms of a model assuming that stimulus color and location are processed independently. Subjects attend to the dimension resolved most quickly which can reliably specify the target.     

Can certain stimulus characteristics influence the hemispheric differences in global and local processing?

Hemispheric processing of global and local form was examined in two experiments in which the size of hierarchical visual stimuli was manipulated in divided-attention tasks. In experiment 1, the subjects were instructed to decide whether or not a symmetrical target (T) was in the visual object presented. In experiment 2, the target to be detected was nonsymmetrical (L). In both studies, global precedence was found depending on stimulus size. When the stimuli subtended about 3 degrees vertically, global dominance was found, but it was not detected when the stimuli subtended about 10 degrees. Experiments 1 and 2 provided evidence against the analytic/holistic dichotomy, presenting the same performance for both hemispheres: the global analysis was much better than the local analysis. When the target was in the global form, both the LH and the RH analyzed the 3 degrees stimuli more efficiently, while both analyzed the 10 degrees stimuli with greater efficiency when the target was in the local form.     

Influence of stimulus type on effects of flanker,flanker position,and trial sequence in a saccadic eye movement task

Using the flanker paradigm in a task requiring eye movement responses, we examined how stimulus type (arrows vs. letters) modulated effects of flanker and flanker position. Further, we examined trial sequence effects and the impact of stimulus type on these effects. Participants responded to a central target with a left- or rightward saccade. We reasoned that arrows, being overlearned symbols of direction, are processed with less effort and are therefore linked more easily to a direction and a required response than are letters. The main findings demonstrate that (a) flanker effects were stronger for arrows than for letters, (b) flanker position more strongly modulated the flanker effect for letters than for arrows, and (c) trial sequence effects partly differed between the two stimulus types. We discuss these findings in the context of a more automatic and effortless processing of arrow relative to letter stimuli.     

Priming effects in perceptual classification

Priming stimuli that spatially flank a fixated target stimulus may cause either facilitation or interference with target classification, depending on experimental context. Two experiments demonstrated distinct effects of response compatibility and semantic congruity between flankers and target. Response competition occurred when targets were flanked by context stimuli associated with the opposite response, but this effect diminished when the target was delayed relative to the flankers. Facilitative priming by response-compatible flankers, in contrast, required prior exposure of the flankers, and was strongly influenced by the semantic congruity of flankers and targets. These differing time courses suggest that perceptual priming encompasses a variety of distinct underlying cognitive and motor events.     

Faces retain attention

In the present study, we investigated whether faces have an advantage in retaining attention over other stimulus categories. In three experiments, subjects were asked to focus on a central go/no-go signal before classifying a concurrently presented peripheral line target. In Experiment 1, the go/no-go signal could be superimposed on photographs of upright famous faces, matching inverted faces, or meaningful objects. Experiments 2 and 3 tested upright and inverted unfamiliar faces, printed names, and another class of meaningful objects in an identical design. A fourth experiment provided a replication of Experiment 1, but with a 1,000-msec stimulus onset asynchrony between the onset of the central face/nonface stimuli and the peripheral targets. In all the experiments, the presence of an upright face significantly delayed target response times, in comparison with each of the other stimulus categories. These results suggest a general attentional bias, so that it is particularly difficult to disengage processing resources from faces.     

Identification and categorization in visual search

Seven experiments were addressed to the general question of whether the identification of letters and numbers is a more rapid process than the categorization of such stimuli. Subjects were required to make a single response if a target stimulus specified by name (e.g., “A,” “2”) or designated by category class alone (e.g., “letter,” “number”) was presented in a trial. The principal findings were: (1) identification reaction times (RTs) were faster than categorization RTs: (2) RTs for targets shown without a context were faster than RTs for targets shown in the context of other stimuli; (3) identification RTs for targets shown in the context of stimuli from a different conceptual-taxonomic category were faster than RTs for targets shown in the context of stimuli from the same category only when target-context stimulus discriminability differencet were optimized. The results were interpreted in terms of a two-stage processing model in which context face,ors affect the duration of an initial encoding-scanning stage and search instruction (effective memory size) factors affect the duration of the memory comparison stage.     

Loci of phonological effects in the lexical access of words written in a shallow orthography

Summary Three experiments are reported that extend previous observations on the slowing of lexical decisions by phonologically ambiguous forms of Serbo-Croatian words relative to the phonologically unambiguous forms of the same words. The phonological ambiguity arises from the presence of letters whose phoneme interpretation differs between the two Serbo-Croatian alphabets, the Roman and the Cyrillic. In the first experiment, target words were preceded by asterisks or by context words that were associatively related and alphabetically matched to the targets. The effect of word contexts (i.e., priming) was greater for phonologically ambiguous than for phonologically unambiguous targets. The second experiment manipulated the alphabetic match of context word and target word. The effect of this manipulation was limited to phonologically ambiguous words. The third experiment reproduced the details of the first with the addition of visual degradation of the target stimuli on half of the trials. The results of the first experiment were replicated but no interaction between context and visual degradation was observed. The discussion focused on phonologically mediated access of Serbo-Croatian words. A model was proposed in which phonological codes are assembled prelexically according to weighted grapheme-phoneme correspondence rules.     

Parallel memory retrieval in dual-task situations: II. Episodic memory

Three experiments asked whether subjects could retrieve information from a 2nd stimulus while they retrieved information from a 1st stimulus. Subjects performed recognition judgments on each of 2 words that followed each other by 0, 250, and 1,000 ms (Experiment 1) or 0 and 300 ms (Experiments 2 and 3). In each experiment, reaction time to both stimuli was faster when the 2 stimuli were both targets (on the study list) or both lures (not on the study list) than when 1 was a target and the other was a lure. Each experiment found priming from the 2nd stimulus to the 1st when both stimuli were targets. Reaction time to the 1st stimulus was faster when the 2 targets came from the same memory structure at study (columns in Experiment 1; pairs in Experiment 2; sentences in Experiment 3) than when they came from different structures. This priming is inconsistent with discrete serial retrieval and consistent with parallel retrieval.