Unilateral hemispheric activation does not affect free-viewing perceptual asymmetries

Strong leftward perceptual biases have been reported for the selection of the darker of two left/right mirror-reversed luminance gradients under free-viewing conditions. This study investigated the effect of unilateral hemispheric activation on this leftward bias in two groups of dextrals (N = 52 and N = 24). In Experiment 1, activation was manipulated by asking participants to tap with their left or right fingers along their midline. In Experiment 2, participants clenched their left or right hands in their respective hemispaces. Participants selected the stimulus that was darker on the left-hand side 73% of the time. Despite manipulations of activation strength and hemispace, activation had no effect on the asymmetry. If activation was important, the leftward bias should have been enhanced when the left hand/right hemisphere was active and reduced (or reversed) when the right hand/left hemisphere was active. The contribution of left-to-right scanning biases to free-viewing perceptual asymmetries is discussed as an alternative.     

Response-to-stimulus interval does not affect implicit motor sequence learning, but does affect performance

Nissen and Bullemer (1987) reported that implicit motor sequence learning was disrupted by the addition of a secondary task. They suggested that this effect was due to the attentional load that the secondary task adds. Recently it has been suggested that the attentional load is not critical, but rather that the secondary task affects timing, either by lengthening or by making inconsistent the response-tostimulus interval (RSI)-that is, the delay between when a subject makes a response and when the next stimulus appears. In six experiments we manipulated the RSI and found no support for these two hypotheses. An inconsistent RSI did not adversely affect implicit motor sequence learning. A long RSI did not affect learning, although under some conditions subjects did not express learning if the RSI was long. These results are interpreted as reflecting the effects of attention.     

Stimulus-set location does not affect orthogonal stimulus-response compatibility

In two-choice tasks for which stimuli and responses vary along orthogonal dimensions, one stimulus-response mapping typically yields better performance than another. For unimanual movement responses, the hand used to respond, hand posture (prone or supine), and response eccentricity influence this orthogonal stimulus-response compatibility (SRC) effect. All accounts of these phenomena attribute them to response-related processes. Two experiments examined whether manipulation of stimulus-set position along the dimension on which the stimuli varied influences orthogonal SRC in a manner similar to the way that response location does. The experiments differed in whether the stimulus dimension was vertical and the response dimension horizontal, or vice versa. In both experiments, an advantage of mapping up with right and down with left was evident for several response modes, and stimulus-set position had no influence on the orthogonal SRC effect. The lack of effect of stimulus-set position is in agreement with the emphasis that present accounts place on response-related processes. We favor a multiple asymmetric codes account, for which the present findings imply that the polarity of stimulus codes does not vary across task contexts although the polarity of response codes does.     

Increasing stimulus intensity does not affect sensorimotor synchronization

When people synchronize taps with isochronously presented stimuli, taps usually precede the pacing stimuli [negative mean asynchrony (NMA)]. One explanation of NMA [sensory accumulation model (SAM), Aschersleben in Brain Cogn 48:66–79, 2002] is that more time is needed to generate a central code for kinesthetic-tactile information than for auditory or visual stimuli. The SAM predicts that raising the intensity of the pacing stimuli shortens the time for their sensory accumulation, thereby increasing NMA. This prediction was tested by asking participants to synchronize finger force pulses with target isochronous stimuli with various intensities. In addition, participants performed a simple reaction-time task, for comparison. Higher intensity led to shorter reaction times. However, intensity manipulation did not affect NMA in the synchronization task. This finding is not consistent with the predictions based on the SAM. Discrepancies in sensitivity to stimulus intensity between sensorimotor synchronization and reaction-time tasks point to the involvement of different timing mechanisms in these two tasks.     

Changing environmental context does not reliably affect memory

Most current theories of human memory propose that context, defined here as the time and place at which an event was experienced, forms an integral feature of the mnemonic representation of events. One way of investigating context is by manipulating the environmental context (which typically means the room in which the experiment takes place). The predominant result of this manipulation reported in the literature has been consistent with theory: Memory performance is better when the learning and testing environments are the same than when they differ. This article reports eight experiments that in aggregate challenge the reliability of this same-context advantage. Experiment 1 reported a failure to obtain a same-context advantage. Experiments 2–7 investigated various features of the design that might have reduced the effect. None of these experiments produced a reliable same-context advantage. Experiment 8 repeated the methodology of a published report of a same-context advantage with more than double the number of subjects, but failed to replicate the effect. An analysis of features of the experiments led to two suggestions for future investigations of the effects of changes in environmental context on memory.     

Movement duration does not affect automatic online control

Pisella et al. (2000) have shown that fast aiming movements are automatically modified on-line in response to a change in target position. Specifically, when a movement is less than 300 ms in duration the reach is completed to a target’s new location even when one never intended to respond to the target jump. In contrast, when movements are slower, the reach is completed according to instructions. At present, it is unclear if it is possible for one’s intentions to guide the initial stages of these slow movements. To determine if the intentional control mechanism can guide the initial stages of a slow aiming movement, participants aimed to targets that could jump at movement onset, with a slow and very slow movement time goal. In particular, participants were to point towards (“pro-point”) or away from (“anti-point”) the target jump, with a movement time goal of 500 or 1200 ms. Results showed that in the anti-point condition, movement trajectories first deviated in the same direction as the target jump, followed by a response in the intended (opposite) direction. This suggests that while movement outcome is controlled by the intentional system, even in these slow aiming movements the automatic system is engaged at movement onset.     

Working memory does not dissociate between different perceptual categorization tasks

Working memory is crucial for many higher level cognitive functions, ranging from mental arithmetic to reasoning and problem solving. Likewise, the ability to learn and categorize novel concepts forms an indispensable part of human cognition. However, very little is known about the relationship between working memory and categorization. This article reports 2 studies that related people's working memory capacity (WMC) to their learning performance on multiple rule-based and information-integration perceptual categorization tasks. In both studies, structural equation modeling revealed a strong relationship between WMC and category learning irrespective of the requirement to integrate information across multiple perceptual dimensions. WMC was also uniformly related to people's ability to focus on the most task-appropriate strategy, regardless of whether or not that strategy involved information integration. Contrary to the predictions of the multiple systems view of categorization, working memory thus appears to underpin performance in both major classes of perceptual category-learning tasks.     

Expectancy and frequency effects on perceptual and motor systems in choice reaction time

Three experiments investigated the effects of expectancy and stimulus frequency in character classification and identification tasks. Both expectancy and frequency were found to have effects on overall response latency, but the two factors had different patterns of interaction with two other experimental variables. The effect of visual quality was larger for low-frequency stimuli than for high-frequency stimuli, whereas the effect of quality was independent of expectancy. The effect of S-R compatibility was more strongly influenced by whether a stimulus was expected than by the frequency of the stimulus. The results suggest that expectancy and frequency have somewhat different effects on human information processing mechanisms. Expectancy allows temporary preparation for a specific S-R pair in response selection processes, but it has no effect on perceptual processes. Stimulus frequency, on the other hand, influences the efficiency of both perceptual and response selection processes. The overall effect of stimulus probability may be interpreted as having as components both expectancy and frequency effects.     

Trunk- and head-centred spatial coordinates do not affect free-viewing perceptual asymmetries

Turning the trunk or head to the left can reduce the severity of leftward neglect. This study sought to determine whether turning the trunk or head to the right would reduce pseudoneglect: A phenomenon where normal participants underestimate the rightward features of a stimulus. Participants made luminance judgements of two mirror-reversed greyscales stimuli. A preference for selecting the stimulus dark on the left was found. The effect of trunk-centred coordinates was examined in Expt. 1 by facing the head toward the display and turning the trunk to the left, right or toward the display. Head-centred coordinates were examined in Expt. 2 by directing the eyes toward the display and then turning the head and trunk. No effect of rotation was observed. It was concluded that the leftward bias for the greyscales task could be based on an object-centred attentional bias or left-to-right eye scanning habits.     

Implementation intention encoding does not automatize prospective memory responding

An implementation intention encoding, one that specifies the concrete situation that is appropriate for initiating an intended action and links that situational cue to the intended action, has been shown to improve prospective memory. One proposed mechanism is that implementation intentions create automatized prospective remembering. This view anticipates that implementation intentions should prevent prospective memory decline in highly cognitively demanding situations. Contrary to this expectation, although implementation intention encoding enhanced prospective memory (Experiments 1 and 2), implementation-intention encoding did not buffer against significant prospective memory decline in high-cognitive-demand conditions (Experiments 1–3), and in Experiment 3, implementation intention encoding produced lower levels of prospective memory performance than did behavioral practice in the high-cognitive-demand situation. We suggest that although implementation intentions may stimulate a strong associative encoding (between an anticipated environmental cue and an intended action), that encoding does not support a completely automatized prospective memory response.     

Causal order does not affect cue selection in human associative learning

Waldmann and Holyoak (1992) presented evidence in support of the claim that cue selection does not emerge in “diagnostic” human learning tasks in which the cues are interpretable as effects and the outcomes as the causes of those effects. Waldmann and Holyoak argued that this evidence presents a major difficulty for associationist theories of learning and instead supports a “causal model” theory. We identify a number of flaws in Waldmann and Holyoak’s experimental procedures and report three new experiments designed to test their claim. In Experiment 1, cue selection was observed regardless of causal order and regardless of whether the cues were abstractly or concretely specified. In Experiments 2 and 3, cue selection was again observed when subjects predicted causes from effects. We conclude that our results are consistent with simple associationist theories of learning but contradict Waldmann and Holyoak’s causal model theory.     

Prior knowledge does not facilitate the perceptual organization of dynamic random-dot patterns

Three classes of models for the origins of perceptual organization—linear independence, cognitive facilitation, and self-organization—were tested by evaluating the effects of stimulus unccrtainty and pattern coherence on the detection of coherent motion in dynamic random-dot patterns. Stimulus patterns consisted of two successive frames of randomly positioned dots in which motion was perceived when the dot positions in successive frames were correlated and displaced. The number of alternative directions axed locations of motion and the degree of coherences correlation) between the two successive frames were manipulated. The effects of stimulus uncertainty were less than predicted by cognitive facilitation models and were less than predicted by one linear independence model Ichoice theory), although similar to the predictions of another linear model (the Peterson, Birdsall, & Fox, 1954, approximation of the optimum Gaussian model). Small, but significant, tendencies toward self-organization rather than linear independence of perceived motion in neighboring locations were indicated by a nonlinear effect of coherence on detection accuracy and by the superior detectability of the direction as compared with the location of motion.     

Explicit risk of getting caught does not affect unethical behavior

Research showed that given the opportunity, people behave dishonestly only to the degree that will allow them to maintain a positive self‐concept. These experiments did not include the probability of getting caught cheating, although in everyday life, this risk always exists. If it is shown that people behave more honestly when faced with an explicit risk of getting caught, the ecological validity of these experiments may be at risk. This study showed that explicit risk, framed as the probability of getting caught or as the complementary probability of not getting caught, did not reduce participants’ dishonest behavior relative to no risk. These findings support the ecological validity of previous research on unethical behavior.     

Embedding lies into truthful stories does not affect their quality

When given the opportunity, liars will embed their lies into otherwise truthful statements. In what way this embedding affects the quality of lies, however, remains largely unknown. This study investigated whether lies that are embedded into truthful stories are richer in detail and contain higher quality details compared to lies that are part of entirely fabricated statements. Participants (N = 111) were asked to provide a statement that was either entirely truthful, entirely fabricated, or had the fabricated element of interest embedded into an otherwise truthful story. Results indicated that lies embedded in a fabricated statement are not qualitatively different from lies embedded in an otherwise truthful statement. Supporting Bayes factors provided moderate to strong evidence for this conclusion. Accordingly, verbal credibility assessment tools based on the verbal content measured in this study may be robust against the embedding of lies.     

Motion-induced blindness does not affect the formation of negative afterimages

Aftereffects induced by invisible stimuli constitute a powerful tool to investigate what type of neural information processing can occur in the absence of visual awareness. This approach has been successfully used to demonstrate that awareness of oriented gratings or translating stimuli is not necessary to obtain a robust orientation-specific or motion-specific aftereffect. We exploit motion-induced blindness (MIB, Bonneh, Cooperman, & Sagi, 2001) to investigate the related question of the influence of visual awareness on the formation of negative afterimages. Our results show that MIB does not affect the persistence and intensity of afterimages. Thus, there is no significant contribution to the formation of afterimages beyond the sites mediating MIB.     

Color term knowledge does not affect categorical perception of color in toddlers

Categorical perception of color is shown when colors from the same category are discriminated less easily than equivalently spaced colors that cross a category boundary. The current experiments tested various models of categorical perception. Experiment 1 tested for categorical responding in 2- to 4-year-olds, the age range for the onset establishment of color term knowledge. Experiment 2 tested for categorical responding in Himba toddlers, whose language segments the color space differently from the way in which the English language does so. Experiment 3 manipulated the conditions of the task to explore whether the categorical responding in Experiments 1 and 2 was equivalent to categorical perception. Categorical perception was shown irrespective of naming and was not stronger in those children with more developed color term knowledge. Cross-cultural differences in the extent of categorical perception were not found. These findings support universalistic models of color categorization and suggest that color term knowledge does not modify categorical perception, at least during the early stages of childhood.