Does ignoring lead to worse evaluations? A new explanation of the stimulus devaluation effect

Affective evaluation of stimuli just seen in visual search tasks has been shown to depend on task-relevant stimulus configuration (Raymond, Fenske, & Tavassoli, 2003): Whereas targets and novel stimuli were evaluated similarly, distractors were devaluated. These results were explained by an inhibition-based account of the influence of selective attention on emotion. In the present experiments, we demonstrated that stimulus devaluation might not be a consequence of attentional inhibition. By simply instructing participants to react to an accepted or rejected stimulus in the visual search task of Experiment 1, we found distractor devaluation in the first case and target devaluation in the second case. We conclude that devaluation of stimuli is mediated by the affective connotation implied by response labels and instructions. This was confirmed in Experiment 2: To-be-ignored stimuli were not devaluated when participants knew that those stimuli would become task-relevant during the experiment.     

Effects of exposure on discrimination of similar stimuli and on memory for their unique and common features

Human participants received exposure to similar visual stimuli (AW and BW) that shared a common feature (W). Experiment 1 demonstrated that subsequent discrimination between AW and BW was more accurate when the two stimuli were preexposed on an intermixed schedule (AW, BW, AW, BW…) than when they were preexposed on a blocked schedule (AW, AW…BW, BW…): the intermixed-blocked effect. Furthermore, memory for the unique features of the stimuli (A and B) was better when the stimuli were preexposed on an intermixed schedule than when they were preexposed on a blocked schedule. Conversely, memory for the common features of the stimuli (W) was better when the stimuli were preexposed on a blocked schedule than when they were preexposed on an intermixed schedule. Experiment 2 again demonstrated the intermixed-blocked effect, but participants were preexposed to the stimuli in such a way that the temporal spacing between exposures to the unique features was equated between schedules. Memory for the unique and common features was similar to that found in Experiment 1. These findings support the proposal that perceptual learning depends on a mechanism that enhances memory for the unique features and reduces memory for common features.     

The intermixed-blocked effect in human perceptual learning is not the consequence of trial spacing

A robust finding in humans and animals is that intermixed exposure to 2 similar stimuli (AX/BX) results in better discriminability of those stimuli on test than does exposure to 2 equally similar stimuli in 2 separate blocks (CX_DX)--the intermixed-blocked effect. This intermixed-blocked effect may be an example of the superiority of spaced over massed practice; in the intermixed, but not the blocked exposure regime, each presentation of a given stimulus (e.g., AX) is separated from the next by the presentation of its partner (BX). Two experiments with human participants replicated the intermixed-blocked effect and showed that the effect was not due to the spacing of exposure trials. A mechanism for the intermixed-blocked effect is proposed, which combines theories from associative learning and memory.     

Attention and relative novelty in human perceptual learning

Four experiments examined the role of attention in human perceptual learning. In Experiment 1, participants were preexposed to a pair of visual (checkerboard) stimuli AX and BX, with common elements X and unique features A and B. A same-different task was then used to assess discrimination of AX and BX and a pair of control stimuli, CY and DY. In addition, participants' eye movements were recorded to assess the role of attentional processes. The results showed that preexposure enhanced discrimination between AX and BX. Furthermore, participants showed greater attention to the preexposed unique features A and B than to the novel unique features C and D, as measured by the eye gaze monitor. Experiments 2 and 3 examined the prediction that perceptual learning is due to the relative familiarity of the common and unique stimulus features. Experiment 4 replicated the intermixed-blocked effect and showed that the way in which AX and BX are presented is also important for perceptual learning. The results generally support the idea that intermixed preexposure to AX and BX increases attention to the unique stimulus features A and B. Some aspects of the results are consistent with a relative novelty account, whereas others implicate a high-level attentional process that is not driven by stimulus novelty.     

Is it dangerous? The role of an emotional visual search strategy and threat-relevant training in the detection of guns and knives

Counter-terrorism strategies rely on the assumption that it is possible to increase threat detection by providing explicit verbal instructions to orient people's attention to dangerous objects and hostile behaviours in their environment. Nevertheless, whether verbal cues can be used to enhance threat detection performance under laboratory conditions is currently unclear. In Experiment 1, student participants were required to detect a picture of a dangerous or neutral object embedded within a visual search display on the basis of an emotional strategy ‘is it dangerous?’ or a semantic strategy ‘is it an object?’. The results showed a threat superiority effect that was enhanced by the emotional visual search strategy. In Experiment 2, whilst trainee police officers displayed a greater threat superiority effect than student controls, both groups benefitted from performing the task under the emotional than semantic visual search strategy. Manipulating situational threat levels (high vs. low) in the experimental instructions had no effect on visual search performance. The current findings provide new support for the language-as-context hypothesis. They are also consistent with a dual-processing account of threat detection involving a verbally mediated route in working memory and the deployment of a visual template developed as a function of training.     

Retrieval conditions and false recognition: testing the distinctiveness heuristic

High levels of false recognition are observed after people study lists of semantic associates that all converge on a nonpresented lure word. In previous experiments, we have found that orienting participants to encode distinctive information about study list items by presenting them as pictures as opposed to words produces marked reductions in false recognition. We have suggested that these reductions reflect the operation of a distinctiveness heuristic: Participants demand access to detailed pictorial information in order to support a positive recognition decision. The present experiments provide additional evidence on this point and allow us to distinguish between the distinctiveness heuristic account and an alternative account based on the impoverished encoding of relational information that occurs when one is studying pictures. In Experiment 1, even when only half of the items in a study list were presented as pictures, a general suppression of false recognition was observed that could be attributable to impoverished encoding of relational information. Experiment 2 provided a critical test of the distinctiveness heuristic account: We manipulated test instructions and found that differences in false recognition rates between picture and word encoding were attenuated in a retrieval condition that did not encourage reliance on a distinctiveness heuristic.     

Effects of spatial and selective attention on basic multisensory integration

When participants respond to auditory and visual stimuli, responses to audiovisual stimuli are substantially faster than to unimodal stimuli (redundant signals effect, RSE). In such tasks, the RSE is usually higher than probability summation predicts, suggestive of specific integration mechanisms underlying the RSE. We investigated the role of spatial and selective attention on the RSE in audiovisual redundant signals tasks. In Experiment 1, stimuli were presented either centrally (narrow attentional focus) or at 1 of 3 unpredictable locations (wide focus). The RSE was accurately described by a coactivation model assuming linear superposition of modality-specific activation. Effects of spatial attention were explained by a shift of the evidence criterion. In Experiment 2, stimuli were presented at 3 locations; participants had to respond either to all signals regardless of location (simple response task) or to central stimuli only (selective attention task). The RSE was consistent with task-specific coactivation models; accumulation of evidence, however, differed between the 2 tasks.     

Mental rotation is not easily cognitively penetrable

When participants take part in mental imagery experiments, are they using their “tacit knowledge” of perception to mimic what they believe should occur in the corresponding perceptual task? Two experiments were conducted to examine whether such an account can be applied to mental imagery in general. These experiments both examined tasks that required participants to “mentally rotate” stimuli. In Experiment 1, instructions led participants to believe that they could reorient shapes in one step or avoid reorienting the shapes altogether. Regardless of instruction type, response times increased linearly with increasing rotation angles. In Experiment 2, participants first observed novel objects rotating at different speeds, and then performed a mental rotation task with those objects. The speed of perceptually demonstrated rotation did not affect the speed of mental rotation. We argue that tacit knowledge cannot explain mental imagery results in general, and that in particular the mental rotation effect reflects the nature of the underlying internal representation and processes that transform it, rather than participants’ pre-existing knowledge.     

Visual search asymmetry: The influence of stimulus familiarity and low-level features

Wang, Cavanagh, and Green (1994) demonstrated a pop-out effect in searching for an unfamiliar target among familiar distractors (U—F search) and argued for the importance of a familiarity difference between the target and the distractors in determining search efficiency. In four experiments, we explored the generality of that finding. Experiment 1 compared search efficiency across a variety of target-distractor pairs. In Experiments 2, 3, and 4, we used Chinese characters and their transforms as targets and distractors and compared search performance between Chinese and non-Chinese participants. We demonstrated that search asymmetry and search efficiency in the U—F condition are influenced by the presence of low-level feature differences between the familiar and the unfamiliar stimuli. Our findings suggest that the familiarity of the distractors, rather than the familiarity difference between the target and the distractors, determines search efficiency. We also documented a counterintuitive familiarity-inferiority effect, suggesting that knowledge of search stimuli may, sometimes, be detrimental to search performance.     

Expectations about stimulus structure in implicit learning

In two experiments, artificial grammar learning was used to create learning tasks of identical symbolic complexity that differed in terms of the instructions and the appearance of the stimuli. In Experiment 1, the stimuli were letter strings that appeared in either upper- or lowercase; however, letter case was irrelevant to the learning task. Participants were unable to take into account the instruction to ignore letter case. In Experiment 2, the stimuli were sequences of cities that corresponded to the routes of a traveling salesman. It was assumed that participants would adopt the expectation that the salesman would prefer short journeys. When the structure of the stimuli was inconsistent with this expectation, performance on the learning task was inhibited. The results suggest that there are circumstances in which explicit expectations about the structure of a set of stimuli can affect implicit learning of the stimuli.     

Acquired equivalence in human discrimination learning: the role of propositional knowledge

The current study investigated the role of propositional knowledge in human acquired equivalence effects. Across 5 experiments, human adults were trained to associate different visual stimuli. Subsequent procedures presented training that was either consistent or inconsistent with the previous associations. More accurate responding in the consistent versus inconsistent condition reflected an acquired equivalence effect. The results of Experiment 1 indicated that a previously reported divergence between verbal and associative processes was likely due to instructional control. Experiments 2-5 further examined the role of verbal processes and demonstrated that acquired equivalence may be produced with verbal instructions alone and critically through a combination of instructions and actual stimulus pairings. The current data not only challenge a purely associative account but actively support an interaction between verbal and associative processes in producing the acquired equivalence effect in humans.     

The contributions of strategy use to working memory span: a comparison of strategy assessment methods

In two experiments, we tested whether individual differences in strategy production account for individual differences in performance on a working memory span task. We measured the strategies used during a standard experimenter-paced operation span (OSPAN) task by having participants make both set-by-set reports of strategy use for individual item sets and global reports of strategy use. In Experiment 1, although normatively effective strategies were self-reported on only a small proportion of OSPAN sets, individual differences in effective strategy use correlated with span performance. Experiment 2 replicated this outcome using a sample of 100 participants but, as important, it demonstrated that individual differences in effective strategy use did not mediate the relationship between OSPAN and measures of verbal ability. Discussion focuses on the interpretation of strategy-span relationships and the relative utility of general reports of strategy use versus the set-by-set reports introduced here for the OSPAN task.     

The contributions of strategy use to working memory span: A comparison of strategy assessment methods

In two experiments, we tested whether individual differences in strategy production account for individual differences in performance on a working memory span task. We measured the strategies used during a standard experimenter-paced operation span (OSPAN) task by having participants make both set-by-set reports of strategy use for individual item sets and global reports of strategy use. In Experiment 1, although normatively effective strategies were self-reported on only a small proportion of OSPAN sets, individual differences in effective strategy use correlated with span performance. Experiment 2 replicated this outcome using a sample of 100 participants but, as important, it demonstrated that individual differences in effective strategy use did not mediate the relationship between OSPAN and measures of verbal ability. Discussion focuses on the interpretation of strategy–span relationships and the relative utility of general reports of strategy use versus the set-by-set reports introduced here for the OSPAN task.     

Visual search asymmetry: the influence of stimulus familiarity and low-level features.

Wang, Cavanagh, and Green (1994) demonstrated a pop-out effect in searching for an unfamiliar target among familiar distractors (U-F search) and argued for the importance of a familiarity difference between the target and the distractors in determining search efficiency. In four experiments, we explored the generality of that finding. Experiment 1 compared search efficiency across a variety of target-distractor pairs. In Experiments 2, 3, and 4, we used Chinese characters and their transforms as targets and distractors and compared search performance between Chinese and non-Chinese participants. We demonstrated that search asymmetry and search efficiency in the U-F condition are influenced by the presence of low-level feature differences between the familiar and the unfamiliar stimuli. Our findings suggest that the familiarity of the distractors, rather than the familiarity difference between the target and the distractors, determines search efficiency. We also documented a counterintuitive familiarity-inferiority effect, suggesting that knowledge of search stimuli may, sometimes, be detrimental to search performance.     

Is it impossible to inhibit isoluminant items, or does it simply take longer? Evidence from preview search

Visual search can be facilitated when participants receive a preview of half the distractors (the preview benefit in search; Watson & Humphreys, 1997). Donk and Theeuwes (2001) have argued that preview-based benefits are abolished if the display items are isoluminant to a background. This is consistent with the preview benefit being due to onset capture by the new stimuli. In contrast, the present experiments challenge this suggestion and show that preview benefits can occur under isoluminant conditions, providing that they are given enough time to occur. In Experiment 1, we showed that a preview benefit can occur even with isoluminant stimuli, provided that the old items are previewed for a sufficient time. In Experiment 2, we tested and rejected the idea that this advantage is due to low-level sensory fatigue for the preview stimuli. These findings indicate that the preview effect is not caused solely by onset capture.     

Searching for threat

In a series of experiments, a visual search task was used to test the idea that biologically relevant threatening stimuli might be recognized very quickly or capture visuo-spatial attention. In Experiment 1, there was evidence for both faster detection and faster search rates for threatening animals than for plants. However, examination of the basis of this effect in Experiment 2 showed that it was not due to threat per se, as detection and search rate advantages were found for pleasant rather than threatening animals compared to plants. In Experiment 3, participants searched for the plants and pleasant and threatening animals used in Experiments 1 and 2, among a fixed heterogeneous selection of non-target items. There was no search rate or detection advantage for threatening animals compared to pleasant animals or plants. The same targets and non-targets as those used in Experiment 3 were also used in Experiment 4. In Experiment 4, participants searched for targets that were presented either close to or distant from an initial fixation point. There was no evidence for a "threat" detection advantage either close to or distant from the cross. Finally, an experiment was conducted in which target categories (fruit, flowers, and animals) were not pre-specified prior to each trial block. There were no differences in reaction times to detect pleasant animals, threatening animals, or fruit. We conclude that the visual search paradigm does not readily reveal any biases that might exist for threatening stimuli in the general population.     

Eye movements and spoken language comprehension: effects of visual context on syntactic ambiguity resolution

When participants follow spoken instructions to pick up and move objects in a visual workspace, their eye movements to the objects are closely time-locked to referential expressions in the instructions. Two experiments used this methodology to investigate the processing of the temporary ambiguities that arise because spoken language unfolds over time. Experiment 1 examined the processing of sentences with a temporarily ambiguous prepositional phrase (e.g., "Put the apple on the towel in the box") using visual contexts that supported either the normally preferred initial interpretation (the apple should be put on the towel) or the less-preferred interpretation (the apple is already on the towel and should be put in the box). Eye movement patterns clearly established that the initial interpretation of the ambiguous phrase was the one consistent with the context. Experiment 2 replicated these results using prerecorded digitized speech to eliminate any possibility of prosodic differences across conditions or experimenter demand. Overall, the findings are consistent with a broad theoretical framework in which real-time language comprehension immediately takes into account a rich array of relevant nonlinguistic context.     

The influence of extinction and counterconditioning instructions on evaluative conditioning effects

In three experiments, we tested the influence of instructions about an allegedly upcoming extinction or counterconditioning phase on evaluative conditioning (EC) effects. After an acquisition phase in which neutral stimuli were related to positive or negative stimuli via instructions (Experiments 1 and 2a) or actual pairings (Experiment 2b), three different groups of participants were either informed that in the next phase the neutral stimuli would be presented without positive or negative stimuli (extinction instruction), that the neutral stimuli in the next phase would be paired with stimuli of the opposite valence than before (counterconditioning instruction), or received no further instructions. Afterwards, liking of the originally neutral stimuli was measured either with an evaluative rating (Experiment 1) or with an Implicit Association Test (IAT; Experiments 2a and 2b). EC was reduced in the counterconditioning condition of Experiment 1 and in the joint analysis of Experiments 2a and 2b. The extinction instruction led to a reduction of EC only in Experiment 1. Finally, whether the acquisition phase consisted of instructions about CS–US pairings (Experiment 2a) or the actual experience of CS–US pairings (Experiment 2b) did not significantly impact the observed changes in liking. Overall, our results suggest that similar mechanisms might mediate instruction- and experienced-based EC. Our results are in line with propositional models of EC but can be explained also by association formation models and dual process models of EC, provided that certain auxiliary assumptions are made.     

The Simon Effect With Wheel-Rotation Responses

The authors examined clockwise and counterclockwise wheel-rotation responses to high- or low-pitched tones presented in participants' (N = 96, Experiment 1; N = 48, Experiment 2; N = 48, Experiment 3) left and right ears. In Experiment 1, a Simon effect (fastest responding when tone location and direction of wheel turn corresponded) was obtained when participants' hands were at the top or middle of the wheel but not at the bottom. With line bottom hand placement, a Simon effect was induced by instructions emphasizing hand movements but not by instructions emphasizing wheel movements (Experiment 2), and by a visual cursor controlled by the wheel but not one triggered by the response (Experiment 3). The results of the experiments showed that the nature of the task and the instructed action goal influence the direction of the Simon effect.