Visual and auditory accessory stimulus offset and the Simon effect

We investigated the effect on the right and left responses of the disappearance of a task-irrelevant stimulus located on the right or left side. Participants pressed a right or left response key on the basis of the color of a centrally located visual target. Visual (Experiment 1) or auditory (Experiment 2) task-irrelevant accessory stimuli appeared or disappeared at locations to the right or left of the central target. In Experiment 1, responses were faster when onset or offset of the visual accessory stimulus was spatially congruent with the response. In Experiment 2, responses were again faster when onset of the auditory accessory stimulus and the response were on the same side. However, responses were slightly slower when offset of the auditory accessory stimulus and the response were on the same side than when they were on opposite sides. These findings indicate that transient change information is crucial for a visual Simon effect, whereas sustained stimulation from an ongoing stimulus also contributes to an auditory Simon effect.     

Inhibition and decay of motor and nonmotor priming

Motor responses can be facilitated by congruent visual stimuli and prolonged by incongruent visual stimuli that are made invisible by masking (direct motor priming). Recent studies on direct motor priming showed a reversal of these priming effects when a three-stimulus paradigm was used in which a prime was followed by a mask and a target stimulus was presented after a delay. A similar three-stimulus paradigm on nonmotor priming, however, showed no reversal of priming effects when the mask was used as a cue for processing of the following target stimulus (cue priming). Experiment 1 showed that the time interval between mask and target is crucial for the reversal of priming. Therefore, the time interval between mask and target was varied in three experiments to see whether cue priming is also subject to inhibition at a certain time interval. Cues indicated (1) the stimulus modality of the target stimulus, (2) the task to be performed on a multidimensional auditory stimulus, or (3) part of the motor response. Whereas direct motor priming showed the reversal of priming about 100 msec after mask presentation, cue priming effects simply decayed during the 300 msec after mask presentation. These findings provide boundary conditions for accounts of inverse priming effects.     

The influence of expertise and of physical complexity on visual short-term memory consolidation

We investigated whether the expertise of a perceiver and the physical complexity of a stimulus influence consolidation of visual short-term memory (VSTM) in a S1-S2 (Stimulus 1-Stimulus 2) change detection task. Consolidation is assumed to make transient perceptual representations in VSTM more durable, and it is investigated by postexposure of a mask shortly after offset of the perceived stimulus (S1; 17 to 483?ms). We presented colours, Chinese characters, pseudocharacters, and novel symbols to novices (Germans) or experts of Chinese language (Chinese readers). Physical complexity was manipulated by the number of strokes. Unfamiliar material was remembered worse than familiar material (Experiments 1, 2, and 3). For novices the absolute VSTM performance was better for physically simple than for complex material, whereas for experts the complexity did not matter-Chinese readers memorized Chinese characters (Experiment 3). Articulatory suppression did not change these effects (Experiment 2). We always observed a strong effect of SOA, but this effect was influenced neither by physical complexity nor by expertise; only the length of the interstimulus interval between S1 and the mask was relevant. This was observed even with short stimulus onset asynchrony (SOA) of 100?ms (Experiment 2) and in comparing colours and characters (Experiment 5). However, masks impaired memory if they were presented at the locations of the to-be-memorized items, but not beside them-that is, interference was location-based (Experiment 6). We explain the effect of SOA by the assumption that it takes time to stop encoding of information presented at item locations with the offset of S1. The increasing resistance against interference by irrelevant material appears as consolidation of S1.     

Fixation disengagement and eye-movement latency

We examined eye-movement latencies to a target that appeared during visual fixation of a stationary stimulus, a moving stimulus, or an extrafoveal stimulus. The stimulus at fixation was turned off either before target onset (gap condition) or after target onset (overlap condition). Consistent with previous research, saccadic latencies were shorter in gap conditions than they were in overlap conditions (the gap effect). In Experiment 1, a gap effect was observed for vergence eye movements. In Experiment 2, a gap effect was observed for saccades directed at a target that appeared during visual pursuit of a moving stimulus. In Experiment 3, a gap effect was observed for saccades directed at a target that appeared during extrafoveal fixation. The present results extend reports of the gap effect for saccadic shifts during visual fixation to (a) vergence shifts during visual fixation, (b) saccadic shifts during smooth visual pursuit, and (c) saccadic shifts during extrafoveal fixation. The present findings are discussed with respect to the incompatible goals of fixation-locking and fixation-shifting oculomotor responses.     

Saccade latency and warning signals: Stimulus onset,offset, and change as warning events

Two experiments investigated saccade latency to a peripheral target under various warning signal conditions. In Experiment I, the effects of warning stimulus onset, change, and two offset conditions were compared at warning intervals of 0, 100, 300, and 600 msec. Warning stimulus onset, change, and offset were all effective in reducing saccade latency as compared to a no-warning control condition, but warning stimulus offset resulted in shorter saccade latency than onset or change at all warning intervals. Experiment 2 compared onset and offset warning conditions at ?300-, ?250-, ?200-, ?150-, ?100-, ?50-, 0-, and 50-msec intervals. Responses following onset were slower than those following offset at the latter five intervals, while warning onset resulted in slower saccades than no-warning control conditions at ?150-, ?100-, and ?50-msec intervals. These results indicate that the onset of a visual warning signal can have an interfering effect on the programming or execution of a saccade.     

Modulation of inhibition of return by type and number of dynamic changes of the cue

Inhibition of return (IOR) is a response delay when the target is preceded by an irrelevant stimulus (cue) at the same location. In a previous study, we investigated the separate and joint effects on IOR of cue onset and offset. IOR was much greater when cue onset was followed by cue offset (on-off cue) than when the cue was a single event (on or off cues). The aim of the present study was to test whether the greater IOR with an on-off cue is due to the presence of two cue events. Three experiments were conducted. In Experiment 1 we replicated, with a different delay between cue onset and offset, the finding that IOR is greater with an on-off cue than with a single cue event. In Experiments 2 and 3, we used cues formed by two events. In Experiment 2, an on-off cue was compared with an off-on cue, whereas in Experiment 3 an on-on cue was compared with an off-off cue. Results showed that the magnitude of IOR did not simply depend on the number of cue events occurring before the target. IOR was greater with two different events than with two identical events and greater when was preceded by an off-event than an on-event. Therefore, IOR was greatest with an on-off cue, which likely also benefited from a gap effect. Possible mechanisms underlying IOR were discussed. Received: 31 March 1999 / Accepted: 23 July 1999     

Backward masking by pattern stimulus offset

The backward masking effects of the offset of a pattern stimulus on the apparent contrast of a target stimulus were determined to be a function of target onset-mask offset asynchrony. With spatially overlapping stimuli and binocular viewing, a monotonic function similar to that characterizing early dark adaptation was obtained; with a dichoptically presented disk onset as target and a surrounding ring offset as mask, a typical U-shaped metacontrast effect as a function of target onset-mask offset asynchrony was obtained. These mask-offset effects are related to the possible roles of (a) peripheral "off" mechanisms and (b) central metacontrast mechanisms in terminating visual response persistence in sustained channels.     

Switching attention within and between categories: Evidence for intracategory inhibition

In a variation of the Posner and Snyder (1975b) paradigm, subjects made speeded “same” or “different” responses to pairs of digits or letters on the basis of name identity (Experiment 1) or physical identity (Experiment 2). Each target pair was preceded by an informative (letter or digit) or noninformative (plus-sign) warning signal. The letter or digit represented by an informative warning signal had a high probability of appearing in the subsequent target pair (expected condition). On trials in which the expected stimulus did not appear in the target pair, the target pair belonged with equal probability to either the same category (either letters or digits) as the expected stimulus or to the opposite category (unexpected-similar and unexpected-opposite conditions, respectively). The pattern of “benefits” and “costs” of attentional expectancy found by Posner and Snyder for “same” responses was replicated: Subjects were faster and more accurate in the expected condition than in the neutral (uninformative warning signal) condition, but slower and less accurate in the unexpected conditions. Present theoretical interest concerns “same” response times and accuracy for the two unexpected conditions. Under instructions emphasizing accuracy as well as speed (Experiments 1 and 2), performance was worse in the unexpected-similar condition than in the unexpected-opposite condition. Only when instructions deemphasized accuracy (Experiment 2) was performance better in the unexpected-similar condition than in the unexpected-opposite condition. The fact that subjects may have more difficulty switching attention within a category than between categories (at least when instructions emphasize accuracy as well as speed) contrasts sharply with current theoretical emphasis on intracategorical facilitation effects in the priming paradigm. The results are interpreted within the framework of a model of attention (Keele & Neill, 1978) in which the activation of associates to the focus of attention is actively and optionally suppressed so as to reduce present or potential interference with the focal information processing.     

Priming of mental operations by masked stimuli

Motor responses can be affected by visual stimuli that have been made invisible by masking. Can masked visual stimuli also affect nonmotor operations that are necessary to perform the task? Here, I report priming effects of masked stimuli on operations that were cued by masking stimuli. Cues informed participants about operations that had to be executed with a forthcoming target stimulus. In five experiments, cues indicated (1) the required response, (2) part of the motor response, (3) the stimulus modality of the target stimulus, or (4) the task to be performed on a multidimensional stimulus. Motor and nonmotor priming effects followed comparable time courses, which differed from those of prime recognition. Experiment 5 demonstrated nonmotor priming without prime awareness. Results suggest that motor and nonmotor operations are similarly affected by masked stimuli.     

Reinforcement of inhibitory positional priming by spatial working memory contents

This study examined whether positional priming of pop-out is modulated by spatial working memory (WM). In Experiments 1A and 1B, observers were presented with a to-be-memorized item (Experiment 1A: triangle; Experiment 1B: circle) prior to performing a block of search trials, with triangular stimulus configurations (one target, two distractors) on an underlying elliptical frame. Each search block was followed by a memory test (i.e., memory conditions). In Experiment 1C, the presentation of the memory item (triangle) was immediately followed by the memory test, and the search block was performed after this test (i.e., no-memory condition). It was found that targets presented at a previous target were detected faster and targets presented at a previous distractor location slower, relative to a previous empty (‘neutral’) stimulus location, respectively. While facilitatory position priming was uninfluenced by the memory manipulation, inhibitory positional priming was larger in the memory than no-memory condition, but only when the memory stimulus (triangle) matched the (triangle) configuration formed by the three search items. This finding of larger inhibitory priming under memory conditions provides further evidence that positional priming, rather than being purely bottom-up determined, is open to top-down influences.     

Object substitution masking: when does mask preview work?

When a target is enclosed by a 4-dot mask that persists after the target disappears, target identification is worse than it is when the mask terminates with the target. This masking effect is attributed to object substitution masking (OSM). Previewing the mask, however, attenuates OSM. This study investigated specific conditions under which mask preview was, or was not, effective in attenuating masking. In Experiment 1, the interstimulus interval (ISI) between previewed mask offset and target presentation was manipulated. The basic preview effect was replicated; neither ISI nor preview duration influenced target identification performance. In Experiment 2, mask configurations were manipulated. When the mask configuration at preview matched that at target presentation, the preview effect was replicated. New evidence of ineffective mask preview was found: When the two configurations did not match, performance declined. Yet, when the ISI between previewed mask offset and target presentation was removed such that the mask underwent apparent motion, preview was effective despite the configuration mismatch. An interpretation based on object representations provides an excellent account of these data.     

Capturing focused attention

When attention is diffuse, as in a visual search task, an abrupt onset almost invariably succeeds in capturing attention. But if attention had been cued in advance to a different location, the same onset may then fail to capture attention (Theeuwes, 1991; Yantis and Jonides, 1990). In previous demonstrations, the onset appeared frequently. This may have diminished the onset's novelty, which in turn could have affected its potency in capturing attention. The question we asked was whether preserving the onset's novelty could enhance its capacity in capturing attention, even when attention had been prioritized elsewhere. As in Theeuwes's (1991) study, observers were cued to the target location with a 100%-predictive central arrow cue. The frequency with which visual transients were introduced was varied across experiments. When the onset stimulus appeared frequently (Experiment 1), it indeed failed to capture attention. But when its appearance was relatively infrequent (Experiment 2), capture effects were clearly observed. In Experiment 3, the target appeared in one location throughout the experiment. This would have improved target localization, but an infrequently appearing onset stimulus still successfully captured attention.     

Flanker and Simon effects interact at the response selection stage

The present study aimed at investigating the processing stage underlying stimulus–stimulus (S–S) congruency effects by examining the relation of a particular type of congruency effect (i.e., the flanker effect) with a stimulus–response (S–R) spatial correspondence effect (i.e., the Simon effect). Experiment 1 used a unilateral flanker task in which the flanker also acted as a Simon-like accessory stimulus. Results showed a significant S–S Congruency × S–R Correspondence interaction: An advantage for flanker–response spatially corresponding trials was observed in target–flanker congruent conditions, whereas, in incongruent conditions, there was a noncorresponding trials' advantage. The analysis of the temporal trend of the correspondence effects ruled out a temporal-overlap account for the observed interaction. Moreover, results of Experiment 2, in which the flanker did not belong to the target set, demonstrated that this interaction cannot be attributed to perceptual grouping of the target–flanker pairs and referential coding of the target with respect to the flanker in the congruent and incongruent conditions, respectively. Taken together, these findings are consistent with a response selection account of congruency effects: Both the position and the task-related attribute of the flanker would activate the associated responses. In noncorresponding-congruent trials and corresponding-incongruent trials, this would cause a conflict at the response selection stage.     

Recency-to-primacy shift in cue competition

Three experiments were conducted using a lick-suppression preparation with rats to determine whether temporal and physical context shifts modulate the effectiveness of 2 sequentially trained blocking stimuli. Experiment 1 ascertained that it is possible to obtain blocking by conditioning rats to react to a target cue using 2 different blocking cues, each trained with a single-phase blocking paradigm. Experiment 2 showed that the more recently trained blocking stimulus was more effective (i.e., showed a recency effect) when testing was conducted immediately after training, but a long retention interval attenuated blocking by the most recently trained blocking stimulus and increased blocking by the initially trained blocking stimulus (i.e., a recency-to-primacy shift). This shift from recency to primacy affected in Experiment 2 by varying the retention interval was replicated in Experiment 3 by changing the physical context between training and testing. Taken together, the results indicate that the effectiveness of sequentially trained competing stimuli follows the same recency-to-primacy shift rule that is seen in traditional interference phenomena.     

The role of physical and conceptual properties in preserving object continuity

Six experiments investigated the nature of the object-file representation supporting object continuity. Participants viewed preview displays consisting of 2 stimuli (either line drawings or words) presented within square frames, followed by a target display consisting of a single stimulus (either a word or a picture) presented within 1 of the frames. The relationship between the target and preview stimuli was manipulated. The first 2 experiments found that participants responded more quickly when the target was identical to the preview stimulus in the same frame (object-specific priming). In Experiments 3, 4, 5, and 6, the physical form of the target stimulus (a word or picture in 1 frame) was changed completely from that of either preview stimulus (pictures or words in both frames). Despite this physical change, object-specific priming was observed. It is suggested that object files encode postcategorical information, rather than precise physical information.     

Inhibition of return for target discriminations: the effect of repeating discriminated and irrelevant stimulus dimensions

Inhibition of return (IOR) refers to slowed reaction times when a target repeats in the same location as a preceding stimulus. In four experiments, the participants were presented with two successive stimuli, S1 and S2. In Experiments 1 and 2, the participants made a speeded discrimination of the identity or orientation of both S1 and S2 (Experiment 1) or of S2 only (Experiment 2). An IOR effect occurred for the repetition of stimulus location, but a facilitatory effect occurred if the stimulus remained unchanged or if an overt response was repeated. In Experiments 3 and 4, the participants localized S1 and S2 (Experiment 3) or S2 only (Experiment 4) to the left or right of center. In this case, repeating the same stimulus had no effect: IOR occurred any time stimulus location repeated. These results demonstrate that the expression of IOR is modulated by the repetition of a target object, but only when the task requires the discrimination of that object; when no discrimination is required, IOR is unaffected.     

An action sequence held in memory can interfere with response selection of a target stimulus,but does not interfere with response activation of noise stimuli

Withholding an action plan in memory for later execution can delay execution of another action if the actions share a similar (compatible) action feature (e.g., response hand). We investigated whether this phenomenon, termed compatibility interference (CI), occurs for responses associated with a target as well as responses associated with distractors in a visual selection task. Participants planned and withheld a sequence of keypress responses (with their right or left hand), according to the identity of a stimulus (A), and then immediately executed a keypress response (with their right or left hand) to a second stimulus (B), according to the identity of a target letter appearing alone or among distractor letters. Distractor letters were either response compatible or incompatible with the target and appeared either simultaneously with the target (Experiments 1A and 2) or 100 msec before the target (Experiment 1B). Also, stimulus-response mapping was either 1:1 (Experiment 1) or 2:1 (Experiment 2). Results showed that the response to the Stimulus B target was delayed when it required the same response hand as Stimulus A, as opposed to a different hand. Also, the target reaction time for Stimulus B was greater when the target was flanked by incompatible distractors than when it was flanked by compatible distractors. Moreover, the degree of CI was consistent across the compatible-, incompatible-, and no-distractor conditions, indicating that CI generalizes to responses associated with a target, but not to those associated with distractors. Thus, CI occurs at a response selection, not at a response activation stage. Implications for the code occupation account for CI (e.g., Stoet & Hommel, 1999, 2002) and an alternative account for CI are discussed.     

Place Learning in Virtual Space I: Acquisition, Overshadowing, and Transfer

Three experiments showed that, in virtual space, humans learn to find an invisible target that remains in a fixed location relative to distal cues. Experiment 1 showed that people rapidly learned to locate an invisible target in a computer-generated virtual arena. Participants searched the appropriate place intensely when, on a probe trial, the target was removed. Experiment 2 showed that two groups of participants, one with a visible and one with an invisible target, learned to locate the target in the virtual arena. A probe trial, during which the target was removed, showed that participants from both groups searched the former location of the target in the virtual arena, suggesting the presence of proximal cues did not interfere with place learning. Experiment 3 showed that, following place learning, people directly approach the location of the invisible target from novel start positions. The data were discussed in terms of spatial learning and memory.     

Top-down contingencies of nonconscious priming revealed by dual-task interference

According to the direct parameter specification (DPS) account, reaction time effects of invisible primes depend on top-down control settings directed to targets (Neumann & Klotz, 1994). If this hypothesis holds, effects of invisible primes should decrease in dual-task as compared with single-task conditions: Prior to the primes control settings for the alternative task should be activated, which renders a match between target-directed control settings and primes less likely. In Experiments 1-2 and 4-5, a second task interfered with the validity effect of invisible primes. Control conditions ruled out several alternative explanations. Interference was not due to higher spatial memory loads (Experiments 1 vs. 2), increased numbers of stimuli or responses (Experiments 3-5), or increased response latencies (Experiment 3). If predictable, alternative tasks did not interfere (Experiment 3). The results are in line with the DPS account and less so with some classical definitions of automatic processing (e.g., Posner & Snyder, 1975).     

A PRP-study to determine the locus of target priming effects

Visual stimuli that are made invisible by a following mask can nonetheless affect motor responses. To localize the origin of these target priming effects we used the psychological refractory period paradigm. Participants classified tones as high or low, and responded to the position of a visual target that was preceded by a prime. The stimulus onset asynchrony (SOA) between both tasks varied. In Experiment 1 the tone task was followed by the position task and SOA dependent target priming effects were observed. When the visual position task preceded the tone task in Experiment 2, with short SOA the priming effect propagated entirely to the tone task yielding faster responses to tones on visually congruent trials and delayed responses to tones on visually incongruent trials. Together, results suggest that target priming effects arise from processing before and at the level of the central bottleneck such as sensory analysis and response selection.