Stimulus-response compatibility for absolute and relative spatial correspondence in reaching and in button pressing

Three experiments tested whether stimulus-response (S-R) compatibility might be a function of absolute (as opposed to relative) spatial correspondence-that is, the distance between a stimulus and the place of response. Experiment 1 studied reaching movements toward one of two targets in response to one of six visual stimuli. Stimulus-response pairs that shared relative position were faster than those that did not, and reaction time was faster when the stimulus and one of the potential targets were in close proximity. In Experiment 2 the same effects were found when the hands started from a different position, implicating stimulus target distance, rather than stimulus-hand distance as the critical variable. Experiment 3 employed keypress responses instead of reaches, and the distance effect was nearly absent. The implications of these results are discussed in terms of categorical (e.g. left-right) vs. quantitative (e.g. distance) S-R variables in spatial compatibility.     

Accounting for sequential trial effects in the flanker task: Conflict adaptation or associative priming?

The conflict-control loop theory proposes that the detection of conflict in information processing triggers an increase in cognitive control, resulting in improved performance on the subsequent trial. This theory seems consistent with the robust finding that conflict susceptibility is reduced following correct trials associated with high conflict: the conflict adaptation effect. However, despite providing favorable conditions for eliciting and detecting conflict-triggered performance adjustments, none of the five experiments reported here provide unequivocal evidence of such adjustments. Instead, the results corroborate and extend earlier findings by demonstrating that the conflict adaptation effect, at least in the flanker task, is only present for a specific subset of trial sequences that is characterized by a response repetition. This pattern of results provides strong evidence that the conflict adaptation effect reflects associative stimulus-response priming instead of conflict-driven adaptations in cognitive control.     

On the Role of Vertical Texture Cues in Height Perception

When people judge height from the top looking down they tend to overestimate vertical distance. Initial findings suggest that this perceptual bias may be in part due to the experienced fear of falling. However, previous studies did not control for potentially relevant optical invariants, especially vertical texture gradient cues, that may inform such perceptual judgments. In this study, we examined to what degree texture gradient cues may account for the perceptual bias in height perception. To this end, in 2 different conditions in which vertical texture gradient cues were either present or absent, participants provided distance and size judgments from an elevated position (5.68 m) and from the ground. Results revealed a systematic overestimation of vertical extent and object size when judged from a height. Yet, the absence or presence of texture gradient cues did not differentially influence these judgments. Finally, although fear levels were reported to be larger at the elevated position than on the ground, fear levels did not correlate with the perceptual bias, thereby demanding further research into the mechanisms underlying the perceptual bias in height perception.     

Sustained Attention and Executive Functioning Performance in Attention-Deficit/Hyperactivity Disorder

The aim of this study was to further refine the cognitive phenotype of attention-deficit/hyperactivity disorder (ADHD), with respect to the ability to sustain attention and executive functioning. Participants were 34 boys with ADHD (combined type) and 28 normal controls. The groups were closely matched for age and IQ. All participants were 12 years of age. Both groups performed a computerized sustained attention task and a response interference task. Measures related to speed, accuracy, and time on task were collected. We found that children with ADHD performed slower, less accurately, more impulsively, and with less stability than controls. Both groups produced more errors with increasing time on task, reflecting reduced vigilance. Importantly, no interaction with time on task was found. The overall pattern of results suggests that measures related to accuracy are more informative than measures related to speed of responding in refining the cognitive phenotype of ADHD.     

Response interference and working memory in 12-year-old children.

A group of 69 12-year-old children performed three well-known response interference tasks: the Stroop task, the Eriksen flanker task, and the Simon task. Individual differences in accuracy and speed correlated across the tasks. However, there was no correlation between the interference effects on these three tasks. Stroop interference, but not the Simon or flanker effect, was correlated with working memory capacity, as obtained from the WISC-R. These results may help clarify the nature of ADHD, which is characterized by problems with response interference.     

Establishing consciousness in non-communicative patients: a modern-day version of the Turing test

In a recent study of a patient in a persistent vegetative state, [Owen, A. M., Coleman, M. R., Boly, M., Davis, M. H., Laureys, S., & Pickard, J. D. (2006). Detecting awareness in the vegetative state. Science, 313, 1402] claimed that they had demonstrated the presence of consciousness in this patient. This bold conclusion was based on the isomorphy between brain activity in this patient and a set of conscious control subjects, obtained in various imagery tasks. However, establishing consciousness in unresponsive patients is fraught with methodological and conceptual difficulties. The aim of this paper is to demonstrate that the current debate surrounding consciousness in VS patients has parallels in the artificial intelligence (AI) debate as to whether machines can think. Basically, (Owen et al., 2006) used a method analogous to the Turing test to reveal the presence of consciousness, whereas their adversaries adopted a line of reasoning akin to Searle's Chinese room argument. Highlighting the correspondence between these two debates can help to clarify the issues surrounding consciousness in non-communicative agents.     

Human freezing in response to affective films

Human freezing has been objectively assessed using a passive picture viewing paradigm as an analog for threat. These results should be replicated for other stimuli in order to determine their stability and generalizability. Affective films are used frequently to elicit affective responses, but it is unknown whether they also elicit freezing-like defense responses. To test whether this is the case, 50 participants watched neutral, pleasant and unpleasant film fragments while standing on a stabilometric platform and wearing a polar band to assess heart rate. Freezing-like responses (indicated by overall reduced body sway and heart rate deceleration) were observed for the unpleasant film only. The unpleasant film also elicited early reduced body sway (1–2 s after stimulus onset). Heart rate and body sway were correlated during the unpleasant film only. The results suggest that ecologically valid stimuli like films are adequate stimuli in evoking defense responses. The results also underscore the importance of including time courses in human experimental research on defense reactions in order to delineate different stages in the defense response.     

Context influence on the perception of figures as conditional upon perceptual organization strategies

Two experiments tested the effect of context on figure perception. Subjects were shown rapid sequences of three figures: a prime, a whole, and a part. They were asked to decide if the third figure was a part of the second (Experiment 1) or if the second and third figures were the same or different with respect to a particular angle (Experiment 2). The prime served to establish a context for stimuli that followed to be compared. Priming had influence on the part—whole comparison in Experiment 1, but not on the local comparison in Experiment 2. The results of Experiment 1 were interpreted as evidence for a role of prior information in perceptual organization. Experiment 2 showed that the task must require an integrative perceptual organization strategy for the priming effects to occur.     

Sustained attention and executive functioning performance in attention-deficit/hyperactivity disorder.

The aim of this study was to further refine the cognitive phenotype of attention-deficit/hyperactivity disorder (ADHD), with respect to the ability to sustain attention and executive functioning. Participants were 34 boys with ADHD (combined type) and 28 normal controls. The groups were closely matched for age and IQ. All participants were 12 years of age. Both groups performed a computerized sustained attention task and a response interference task. Measures related to speed, accuracy, and time on task were collected. We found that children with ADHD performed slower, less accurately, more impulsively, and with less stability than controls. Both groups produced more errors with increasing time on task, reflecting reduced vigilance. Importantly, no interaction with time on task was found. The overall pattern of results suggests that measures related to accuracy are more informative than measures related to speed of responding in refining the cognitive phenotype of ADHD.