Representation of serial order in monkeys (Cebus apella)

Cebus monkeys were trained on a five-item serial learning task, symbolized as ABCDE; the initial stages of training were on the shorter subseries AB, ABC, and ABCD. To assess the monkeys' knowledge of the sequential position of each item, pair-wise tests were given to 2 subjects after acquisition of the ABCD series and to 4 subjects after reaching criterion on the ABCDE series. In both tests, the monkeys performed at high levels on the interior pairs, which were BC for the ABCD series, and BC, BD, and CD for the ABCDE series. These results, as well as the orderly relations observed in the pair-wise tests between first-item response latency and first-item position and between second-item response latency and number of missing items, indicated that the monkeys had developed a well-organized internal representation of the four- and five-item series. Although pigeons are also capable of learning four-item and five-item series, they apparently do not develop a comparable representational structure. The disparity between the monkeys' and pigeons' representational competence for serial order is predictable from the difference in their capacities for associative transitivity.     

Motion aftereffects with rotating ellipses

Summary The perceptual outcome and the motion-aftereffect duration generated by the rotation on the frontal plane of an ellipse with a bar depend on whether the bar is placed along the major or the minor axis. When the bar is placed along the minor axis, a stereokinetic transformation occurs, and the pattern looks like a tilting ring with a perpendicular bar moving rigidly with it. Placing the bar along the major axis prevents the stereokinetic transformation: subjects report deformations and relative motion of the bar with respect to the ellipse. We found that motion aftereffects last longer when the bar is placed along the minor rather than along the major axis. A series of experiments was carried out to investigate whether differences in aftereffect duration are related to the stereokinetic transformation. Results seem to suggest that they are not.The authors' names are in alphabetical order.     

On the limits of the matching concept in monkeys (Cebus apella).

Two cebus monkeys, with many years of experience matching a variety of static visual stimuli (forms and colors) within a standard matching-to-sample paradigm, were trained to press a left lever when a pair of displayed static stimuli were the same and to press a right lever when they were different. After learning the same/different task, the monkeys were tested for transfer to dynamic visual stimuli (flashing versus steady green disks), with which they had no previous experience. Both failed to transfer to the dynamic stimuli. A third monkey, also with massive past experience matching static visual stimuli, was tested for transfer to the dynamic stimuli within our standard matching paradigm, and it, too, failed. All 3 subjects were unable to reach a moderate acquisition criterion despite as many as 52 sessions of training with the dynamic stimuli. These results provide further evidence that, in monkeys, the matching (or identity) concept has a very limited reach; they consequently do not support the view held by some theorists that an abstract matching concept based on physical similarity is a general endowment of animals.     

Stimulus context and infant orientation discrimination

In three experiments, the effect of additional "contextual" elements on the discrimination of the orientation of linear and curvilinear segments was investigated with 4-month-old infants. In Experiment 1, paired visual matrices (one which contained some irregularity in orientation of internal elements, vs one which contained no irregularities) were presented. Infants detected irregular matrices significantly better than chance, but such detection was not aided by contextual elements. Discrimination of orientation in Experiment 2 was assessed with a paired-comparison familiarization-novelty paradigm. It was found that the addition of elements here significantly aided discrimination of linear segment orientation, but not curvilinear segment orientation. Experiment 3 investigated why this effect was not found for curvilinear segments; after equating the curvilinear stimuli to linear ones used in Experiment 2 with respect to the closedness of figure, discrimination of curvilinear orientation was observed.     

Common functional pathways for texture and form vision: A single case study

A single case study of a patient, D.M., with a lesion in the region of the right occipito-temporal gyrus is presented. D.M. had well-preserved language and general cognitive abilities. Colour discrimination, contrast sensitivity, gross depth perception, spatial localization, and motion appreciation were within normal limits.On the evaluation of perceptual abilities, he failed to identify two-dimensional shapes from stereoscopic vision, motion, and texture although in all cases he was able to identify the rough area subtended by the shape. These findings are considered in relation to the current anatomical-physiological functional models of vision and it is suggested that D.M.'s deficits provide evidence for the existence in man of a functional pathway involved in the computation of texture and fine aspects of shape, which is distinct from the pathways involved in motion and stereopsis processing on one hand and colour and coarse aspects of form on the other hand.     

Akinetopsia,achromatopsia and blindsight: Recent studies on perception without awareness

The neural substrate of early visual processing in the macaque is used as a framework to discuss recent progress towards a precise anatomical localization and understanding of the functional implications of the syndromes of blindsight, achromatopsia and akinetopsia in humans. This review is mainly concerned with how these syndromes support the principles of organization of the visual system into parallel pathways and the functional hierarchy of visual mechanisms.     

The role of lexical stress in word recognition and pronunciation

Summary In the present paper several studies are reviewed that are relevant to lexical-stress assignment. The questions asked concern the form of representation of stress and its role in the perception and identification of words in auditory and visual word recognition. The role of stress is also considered in the computation of phonology, as are the linguistic and orthographic constraints that influence its assignment during reading.