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.     

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.     

Selective involvement of the auditory-verbal modality in an acquired communication disorder: Benefit from sign language therapy

A 39-year-old female suffered bitemporal infarctions and exhibited an unusual behavioral syndrome of muteness and impaired auditory comprehension, with milder aphasic deficits in reading and writing. The anatomic basis of this modality-selective communication disorder appeared to involve both peripheral perceptual and motor as well as “central” language mechanisms. The patient's ability to communicate was greatly aided by instruction in Amerind and Ameslan Sign Language, in which she learned more than 100 signs. Patients whose acquired language deficits spare modalities of input or output may be ideal candidates for sign language therapy.     

The treatment of epilepsies with Convulsofin

The testing of Convulsofin carried out in 220 patients at 14 clinics over a period of six months confirms the international experience gained with valproic acid and sodium valproinate. The main field of application of Convulsofin according to the experience gained will again be the treatment of fits in generalised primary epilepsy for which it permits to carry out a monotherapy to a remarkable extent. The favourable effect of the preparation in photosensitivity could be confirmed. Also in generalised secondary epilepsy and in fits of partial epilepsy. Convulsofin is partly effective, so that it can recommended as a co-medication in the treatment of therapy-resistant forms of these epilepsies which are difficult to treat. Decrease in thrombocytes, transient increase in serum transaminases, gastrointestinal disorders, loss of hair and undesired increases in body-weight were the more frequently occurring side-effects.     

Right-left confusion in the adult: A verbal labeling effect

Directional judgments are typically slower when relative location is described by the words “east” and “west” or “right” and “left” than when described by the words “north” and “south” or “up” and “down.” A series of experiments are reported that disentangle verbal from perceptual encoding explanations for right-left difficulty. Overall, our results support a verbal encoding explanation for right-left confusion in the adult. Experiments 1-3 demonstrate that in a response-differentiation task, it is response to the labels “north,” “east,” “south,” and “west” that is responsible for right-left confusion. In addition, Experiments 4-6 demonstrate that right-left difficulty in a mirror image discrimination task is contingent on the use of directional labels. (The data also suggest that it may be more difficult to deal with “up,” “down,” “left,” and “right” than with “north,” “south,” “east,” and “west”) The data are interpreted as inconsistent with a bilateral symmetry explanation for right-left confusion.     

The effect of phonemic processing on the retention of graphemic representations for words and nonwords

The three experiments reported in this study were each conducted in two phases. The first phase of Experiment 1 involved a same-different comparison task requiring “same” responses for both mixed-case (e.g., MAIN main) and pure-case (e.g., near near) pairs. This was followed by Phase 2, a surprise recognition test in which a graphemic effect on word retention was indicated by the superior recognition accuracy obtained for pure-case compared with mixed-case pairs. The first phases of Experiments 2 and 3 involved pronounceability and imageability judgment tasks, respectively. Graphemic retention was assessed by contrasting recognition accuracy for letter strings presented, during Phase 2, in their original Phase 1 case, with letter strings presented, during Phase 2, in. a graphemically dissimilar new case. The experiments provided evidence that there was minimal retention of the graphemic representations from which the phonemic representations of words are generated and, further, that the locus of this effect is probably postlexical. Nonwords were recognized more accurately than words in all three experiments. The latter result was attributed to differences between nonwords and words in both graphemic retention and semantic distinctiveness.