Selective attention in the speeded classification and comparison of multidimensional stimuli

Selective attention was studied when subjects were required to make either speeded classifications of single stimuli or comparisons of pairs of multidimensional stimuli. Experiment 1 established that subjects were able to attend selectively to form when the irrelevant dimension of size or shading varied in a speeded-classification (card-sorting) task. Experiment 2 confirmed this finding in a discrete-trials task. However, subjects werenot able to filter out irrelevant dimensional disparity in a comparably designed simultaneous-comparison (i.e., “same”-“different”) task. Mean “same” reaction time increased monotonically with increases in disparity between the two stimuli on the irrelevant dimension. Experiment 3 also revealed a monotonie increase in “same” RT as a function of irrelevant disparity in a successive-comparison task. These results were discussed in terms of a normalization model proposed by Dixon and Just (1978) in which it is assumed that a subject equates the two stimuli on the irrelevant dimension before deciding that they are the same along the relevant dimension. It was concluded that: (1) although subjects can efficiently filter out irrelevant disparity in a speeded-classification task, interference due to irrelevant disparity is obtained in the comparison tasks, (2) a common process such as normalization does not necessarily underlie performance in the speeded-classification and comparison tasks, (3) the ability to attend selectively to a stimulus dimension may be task determined as well as stimulus determined, and (4) contrary to the Dixon and Just proposal, normalization of irrelevant disparity occurs in a comparison task, even when the relevant dimension is represented as a separate encoding feature.     

Contextual effects in vowel perception II: Evidence for two processing mechanisms

Recent experiments have indicated that contrast effects can be obtained with vowels by anchoring a test series with one of the endpoint vowels. These contextual effects cannot be attributed to feature detector fatigue or to the induction of an overt response bias. In the present studies, anchored ABX discrimination functions and signal detection analyses of identification data (before and after anchoring) for an [i]-[I] vowel series were used to demonstrate that [i] and [I] anchoring produce contrast effects by affecting different perceptual mechanisms. The effects of [i] anchoring were to increase within-[i] category sensitivity, while [I] anchoring shifted criterion placements. When vowels were placed in CVC syllables to reduce available auditory memory, there was a significant decrease in the size of the [I]-anchor contrast effects. The magnitude of the [i]-anchor effect was unaffected by the reduction in vowel information available in auditory memory. These results suggest that [i] and [I] anchors affect mechanisms at different levels of processing. The [i] anchoring results may reflect normalization processes in speech perception that operate at an early level of perceptual processing, while the [I] anchoring results represent changes in response criterion mediated by auditory memory for vowel information.     

Robust estimation of ability in the Rasch model

Estimating ability parameters in latent trait models in general, and in the Rasch model in particular is almost always hampered by noise in the data. This noise can be caused by guessing, inattention to easy questions, and other factors which are unrelated to ability. In this study several alternative formulations which attempt to deal with these problems without a reparameterization are tested through a Monte Carlo simulation. It was found that although no one of the tested schemes is uniformly superior to all others, a modified jackknife stood out as the best one in general, it was also super efficient (more efficient than the asymptotically optimal estimator) for tests with forty or fewer items. It is proposed that this sort of jackknifing scheme for estimating ability be considered for practical work.This research was funded through a grant from the Law Enforcement Assistance Administration (78-NI-AX-0047) to the Bureau of Social Science Research, Howard Wainer, Principal Investigator. We would like to thank Ronald Mead, Anne Morgan and James Ramsay for kind, generous, and invaluable help at various stages of the project.     

A comparison of the reliability and validity of the standard MFF and MFF20 with learning-disabled children

A direct comparison was made of the reliability and validity of the standard Matching Familiar Figures Test (MFF) to a recent longer version of the task (MFF20). Subjects comprised two samples of learning-disabled children, matched on age, sex, IQ, and SES. The Salkind and Wright (1977) formulation was used to generate continuous data, and IQ was statistically controlled. Internal reliability estimates showed the MFF20 to be more consistent that the standard version on both error and latency scores. Validity was addressed by comparing the two versions of the task in their ability to predict cognitive and behavioral skills of conceptual relevance to impulsivity. Results indicated that the MFF20 is a more sensitive predictor of academic achievement and attention as observed in a natural setting than is the standard version of the task.This study was supported by a contract (300-77-0495) from the Bureau of Education for the Handicapped, Office of Education, for the University of Virginia Learning Disabilities Research Institute. The authors would like to express appreciation to the school officials who generously assisted in the present study: Elizabeth Bailey, Thomas Cox, Charles Dempsey, Julian King.     

Attitudes Toward Male Oral Contraceptives: Implications for Models of the Relationship Between Beliefs and Attitudes1

Four factors (effectiveness, health risks, cost, and convenience) were orthogonally manipulated in a 3 × 2 × 2 × 2 factorial design to determine their relative importance in influencing attitudes toward and intentions to use male oral contraceptives. The experimental design also permitted a test of the assumption of additivity underlying expectancy-value models of attitude and the assumption of absence of context effects. Results were consistent with expectancy-value models of the relationship between beliefs and attitudes. In addition, it was found that health risks and effedtiveness, in that order, were the most important factors influencing receptivity to male oral contraceptives, with the effects of cost and convenience being mediated by these two factors. Sex differences in attitudes toward male oral contraceptives were also observed.     

Effective random seeding of random number generators

To obtain different sequences of values from a random number generating algorithm, we must start with different seed values or discard a variable number of initial samples. For maximum independence among sequences, differences must include the lowest order seed bits, and some generators require one to wait many samples for differences to propagate to the significant bits. While it is straightforward to generate two statistically independent sequences, it is surprisingly difficult to generate three or more such sequences.