Pierre Jolicoeur

A Solution to the Effect of Sample Size on Outlier Elimination

Results from a Monte Carlo study demonstrate how a non-recursive, a simple recursive, a modified recursive, and a hybrid outlier elimination procedure are influenced by population skew and sample size. All the procedures are based on computing a mean and a standard deviation from a sample in order to determine whether an observation is an outlier. Miller (1991) showed that the estimated mean produced by the simple non-recursive procedure can be affected by sample size and that this effect can produce a bias in certain kinds of experiments. We extended this result to the other three procedures. We also create two new procedures in which the criterion used to identify outliers is adjusted as a function of sample size so as to produce results that are unaffected by sample size.

The time to name disoriented natural objects

A series of experiments revealed systematic effects of orientation on the time required to identify line drawings of natural objects. Naming time increases as patterns are rotated further from the upright. With practice, however, the effect of orientation is reduced considerably. Furthermore, the reduced orientation effect with practice on a set of objects does not transfer to a new set of objects, suggesting that the acquired ability to reduce the orientation effect is specific to particular patterns. Finally, for departures in orientation from the upright between 0° and 120°, the magnitude of the orientation effect on identification for patterns seen for the first time is equivalent to that found in a mental rotation task using the same patterns (making left/right decisions about rotated patterns). This final result suggests that novel depictions of a known class of objects may be identified by a process of mental rotation.

Pictures and names: Making the connection ☆

Abstract In order to identify an object sensory input must somehow access stored information. A series of results supports two general assertions about this process: First, objects are identified first at a particular level of abstraction which is neither the most general nor the most specific possible. Time to provide names more general than “entry point” names is predicted by the degree of association between the “entry point” concept and the required name, not by perceptual factors. In contrast, providing more specific names than that corresponding to the “entry point” concept does require more detailed perceptual analysis. Second, the particular entry point for a given object covaries with its typicality, which affects whether or not the object will be identified at the “basic” level. Atypical objects have their entry point at a level subordinate to the basic level. The generality and usefulness of the notion of “basic level” is discussed in the face of these results.

A central capacity sharing model of dual-task performance.

The authors present the central capacity sharing (CCS) model and derive equations describing its behaviors to explain results from dual-task situations. The predictions of the CCS model are contrasted with those of the central bottleneck model. The CCS model predicts all of the hallmark effects of the psychological refractory period (PRP) pardigm: -1 slope of the PRP effect at short stimulus onset asynchronies (SOAs), underadditivity of precentral Task 2 manipulations, additivity of central or postcentral Task 2 manipulations with SOA, and carry forward to Task 2 of Task 1 precentral or central manipulations at short SOAs. The CCS model also predicts that Task 1 response times increase with decreasing SOA. The model is a viable alternative to the central bottleneck model.

Modulation of the attentional blink by on-line response selection: Evidence from speeded and unspeeded Task1 decisions

Two critical target stimuli (T1 and T2) were embedded in a stream of white letters shown on a black background, using a rapid serial visual presentation paradigm (RSVP, 100 msec/item). T1 was a red H or S; T2 was an X or a Y. Performance in a two-alternative discrimination on T2 was impaired when processing of T1 was required—a result often called an attentional blink (AB). In previous work, the response in Task1 has been an unspeeded and delayed response at the end of the trial. Three experiments compared performances in Task2 that depended on whether Task1 required an unspeeded delayed response or a speeded immediate response. A larger AB was found when a speeded response was required. Furthermore, in the speeded conditions, faster responses in Task1 were associated with a smaller and shorter AB effect than were slower responses. The results show that manipulations affecting a relatively late stage of processing—response selection—affect the magnitude and duration of the AB phenomenon. A new central inhibition theory is proposed to account for these results. According to this theory, the AB is similar to the psychological refractory period effect and is caused by central postponement of short-term consolidation of T2.

Long-term electrophysiological changes in athletes with a history of multiple concussions

Primary objective: This event-related potentials study investigated the long-term effects associated with a history of one or multiple concussions on the N2pc and P3 components using a visual search oddball paradigm. Methods and procedure: A total of 47 university football players were assigned to three experimental groups based on prior concussion history: Athletes with a history of one concussion (single-concussion group); Athletes with two or more concussions (multi-concussion group); non-concussed athletic controls. The average post-concussion period was 31 months for athletes in the multi-concussion group and 59 months for the single-concussion group. Results: This study found significantly suppressed P3 amplitude in the multi-concussed athletes group compared to the single-concussion and non-concussed athletes even when using the time since the latest concussion as a covariate. Conclusion: This finding suggests that the multi-concussed athletes group showed long-lasting P3 amplitude suppression when compared with single-concussion or non-concussed athletes despite equivalent neuropsychological test scores and post-concussion symptoms self-reports. This pattern of results is important because it shows that ‘old’ concussions do not cause general or ubiquitous electrophysiological suppression. The specificity of the long-term effects of previous concussions to the P3, along with an intact N2pc response, suggests that further work may allow one to pinpoint the cognitive system that is specifically affected by multiple concussions.

Restricted attentional capacity between sensory modalities.

The purpose of the experiments was to demonstrate an attentional-blink (AB) effect in a visual second task following the processing of a simple auditory signal. Subjects monitored a stream of letters presented at the middle of a computer screen using rapid serial visual presentation for the presence of a visual target (an X or a Y). In experimental trials, the visual target followed a pure tone that required an immediate speeded-choice response. When the tone had to be processed, accuracy in the visualencoding task suffered a marked and prolonged deficit that was timelocked to the onset of the tone. When the tone could be ignored or when no tone was presented, no deficit was observed in the visual task. The results demonstrate a cross-modal AB effect produced by a simple two-choice auditory discrimination task. The results are consistent with the view that at least part of the AB effect has a central, amodal, postperceptual locus.

Tracking the location of visuospatial attention in a contingent capture paradigm

Currently, there is considerable controversy regarding the degree to which top-down control can affect attentional capture by salient events. According to the contingent capture hypothesis, attentional capture by a salient stimulus is contingent on a match between the properties of the stimulus and top-down attentional control settings. In contrast, bottom-up saliency accounts argue that the initial capture of attention is determined solely by the relative salience of the stimulus, and the effect of top-down attentional control is limited to effects on the duration of attentional engagement on the capturing stimulus. In the present study, we tested these competing accounts by utilizing the N2pc event-related potential component to track the locus of attention during an attentional capture task. The results were completely consistent with the contingent capture hypothesis: An N2pc wave was elicited only by distractors that possessed the target-defining attribute. In a second experiment, we expanded upon this finding by exploring the effect of target-distractor similarity on the duration that attention dwells at the distractor location. In this experiment, only distractors possessing the target-defining attribute (color) captured visuospatial attention to their location and the N2pc increased in duration and in magnitude when the capture distractor also shared a second target attribute (category membership). Finally, in three additional control experiments, we replicated the finding of an N2pc generated by distractors, only if they shared the target-defining attribute. Thus, our results demonstrate that attentional control settings influence both which stimuli attract attention and to what extent they are processed.

Curve tracing: A possible basic operation in the perception of spatial relations

The two experiments in this study suggest that fast internal tracing of curves is employed by the visual system in the perception of certain shape properties and spatial relations. The experimental task in the first experiment was to determine, as rapidly as possible, whether two Xs lay on the same curve or on different curves in a visual display. Mean response time for “same” responses increased monotonically with increasing distance along the curve between the Xs. The task in the second experiment was to decide either that a curve joining two Xs was unbroken or that the curve had a gap. Decision times again increased as the length of the curve joining the Xs was increased. The results of both experiments suggest that people can trace curves in a visual display internally at high speed (the average rate of tracing was about 40° of visual angle per second). Curve tracing may be an important visual process used to integrate information from different parts of a visual display.

A lifetime asymptotic growth curve for human height

A new seven-parameter asymptotic growth curve has been applied to longitudinal data on the height of 13 boys and 14 girls from 1 month to 19 years of age. The residual sums of squares with this new curve were 7.5 times lower on the average than with the currently-used five-parameter curve No. 1 of Preece and Baines (1978, Annals of Human Biology 5, 1-24) and 2.4 times lower than with the recent six-parameter curve of Shohoji and Sasaki (1987, Growth 51, 432-450). The new curve is expressed with respect to total age, passes through the origin, and fits infants as satisfactorily as older children.