Simulation study of a decision-making model of squash competition, phase two: Testing the model through the use of computer simulation

This study aims at verifying the inner validity and logic of a squash competition decision-making model through the use of computer simulation. The model defines the cognitive-decisional strategy of the defending player (D) when selecting a motor reaction in response to his opponent's shot. Computer simulation of the model was carried out on a PDP-10 computer using a recent version of UCI-LISP. Protocol analysis data pertaining to the nature of the information D processes when awaiting the attacking player's shot were fed into the simulation program in order to examine the extent to which the model can reproduce decisions reached in various defensive contexts. Simulation results reveal that the proposed model can account for a substantial part of the variation in the speed and accuracy of D's motor reaction in real sport situations. Several factors like time pressure, expectancies, uncertainty, recency and familiarity of the relationship between signal and response appear to affect D's motor response via the cognitive-decisional strategy employed by the defending player. Particular discrepancies observed between simulation results and decisions reached by expert players in specific defensive situations nevertheless indicate that the decision rule utilized within the present model needs to be refined. In this regard, several issues are discussed and suggestions for further simulation studies are put forward in order to account more precisely for the various features characterizing the defensive player's motor reaction in real sporting context.     

Distractor clustering enhances detection speed and accuracy during selective listening

The effects of distractor clustering on target detection were examined in two experiments in which subjects attended to binaural tone bursts of one frequency while ignoring distracting tones of two competing frequencies. The subjects pressed a button in response to occasional target tones of longer duration (Experiment 1) or increased loudness (Experiment 2). In evenly spaced conditions, attended and distractor frequencies differed by 6 and 12 semitones, respectively (e.g., 2096-Hz targets vs. 1482- and 1048-Hz distractors). In clustered conditions, distractor frequencies were grouped; attended tones differed from the distractors by 6 and 7 semitones, respectively (e.g., 2096-Hz targets vs. 1482- and 1400-Hz distractors). The tones were presented in randomized sequences at fixed or random stimulus onset asynchronies (SOAs). In both experiments, clustering of the unattended frequencies improved the detectability of targets and speeded target reaction times, Similar effects were found at fixed and variable SO As. Results from the analysis of stimulus sequence suggest that clustering improved performance primarily by reducing the interference caused by distractors that immediately preceded the target.     

Additive latency effects of selective and nonselective restricted priming types

The purpose of this investigation was to examine further the contention of Alain et al. (1988) that a third priming type exists, called nonselective restricted (NSR) and controlled by response probability, which is distinct from those types influenced by foreperiod duration (nonselective general priming) and prediction probability (selective priming). In a four-choice reaction time (RT) task, prediction probability (.5, .7, & .9, indicating the likelihood of a particular response) and response probability (.5, .9, denoting the likelihood that a response would be needed at all) exerted significant but noninteractive effects on RTs for prepared responses (most probable), suggesting that each of these probabilities influence different priming types (Sternberg, 1969; selective and NSR, respectively). This was further indicated by the fact that prediction probability, but not response probability, significantly altered RTs for the unprepared (lesser probable) responses. Finally, the hypothesized nonselective character of NSR priming (i.e., all outputs controlled by response probability are equally affected by its value changes) was supported when responses were equiprobable, and, while the null effect of response probability just mentioned seemingly argued against this property when selective priming took place, the interpretation provided herein negated this opposition.     

Computing Cohen’s kappa coefficients using SPSS MATRIX

This short paper proposes a general computing strategy to compute Kappa coefficients using the SPSS MATRIX routine. The method is based on the following rationale. If the contingency table is considered as a square matrix, then the observed proportions of agreement lie in the main diagonal’s cells, and their sum equals the trace of the matrix, whereas the proportions of agreement expected by chance are the joint product of marginals. The generalization to weighted kappa, which requires an additional square matrix of disagreement weights, both matrices having the same order, becomes possible by the use of the Hadamard product-that is, the elementwise direct product of two matrices.     

Determinants of lexical access in speech production: Role of word frequency and age of acquisition

The main determinants of lexical access in speech are considered to be a word's age of acquisition (AoA) and its frequency of occurrence in a speaker's experience. It is unclear whether and how these variables interact, although they are commonly observed to be correlated, for the few studies that address the issue have reported inconsistent findings. An influential view of AoA in lexical processing (Ellis and Lambon Ralph, 2000) predicts stronger frequency effects for items acquired later in life than for those acquired at an early age. Five experiments were designed to investigate the possible interaction of AoA and frequency effects in speech. We found that the interaction between word frequency and AoA was not robust and that, contrary to expectation, the effect of word frequency was greater for words acquired earlier in life than for those acquired later. The implications of our findings are discussed.     

A method to monitor upper limb movement direction encoding in the corticomotor pathway

ABSTRACT Abnormal shoulder and elbow muscle coactivation patterns, or muscle synergies, are commonly present following stroke and may arise through dysfunctional descending neural control from the cortex. The authors evaluated a novel technique for examining corticomotor movement encoding of the upper limb in three dimensions. A 6-degree-of-freedom loadcell recorded arm twitch responses in healthy adults following stimulation over the cortex or over Erb's point in the periphery. Stimuli were delivered while the arm generated a 5 N preload in each of the 6 axial directions. The initial force twitch response to stimulation was used to construct twitch direction vectors for each preload direction. General linear mixed model analyses were used to determine the influence of stimulation location, preload direction, posture, and stimulation intensity on twitch direction. Cortical stimulation gave rise to arm twitch responses that were predictably modified by preload direction. Peripheral stimulation elicited stereotypical twitches that were not influenced by preload. Our stimulation, recording, and analysis techniques were able to capture movement encoding of the upper limb in three dimensions. Such techniques could be utilized in the stroke population to determine and monitor the presence of upper limb synergies during muscle activation.