We compared the ability of psychophysical observers and single cortical neurons to discriminate weak motion signals in a stochastic visual display. All data were obtained from rhesus monkeys trained to perform a direction discrimination task near psychophysical threshold. The conditions for such a comparison were ideal in that both psychophysical and physiological data were obtained in the same animals, on the same sets of trials, and using the same visual display. In addition, the psychophysical task was tailored in each experiment to the physiological properties of the neuron un-der study; the visual display was matched to each neuron’s preference for size, speed, and direction of motion. Under these conditions, the sensitivity of most MT neurons was very similar to the psychophysical sensitivity of the animal observers. In fact, the responses of single neurons typically

& These experiments use functional magnetic resonance imaging (fMRI) to reveal neural activity uniquely associated with perception of biological motion. We isolated brain areas activated during the viewing of point-light figures, then compared those areas to regions known to be involved in coherent-motion perception and kinetic-boundary perception. Coherent motion activated a region matching previous reports of human MT/MST complex located on the temporo-parietooccipital junction. Kinetic boundaries activated a region posterior and adjacent to human MT previously identified as the kinetic-occipital (KO) region or the lateral-occipital (LO) complex. The pattern of activation during viewing of biological

In 3 experiments, the authors investigated the ability of observers to extract the probabilities of successive shape co-occurrences during passive viewing. Participants became sensitive to several temporal-order statistics, both rapidly and with no overt task or explicit instructions. Sequences of shapes presented during familiarization were distinguished from novel sequences of familiar shapes, as well as from shape sequences that were seen during familiarization but less frequently than other shape sequences, demonstrating at least the extraction of joint probabilities of 2 consecutive shapes. When joint probabilities did not differ, another higher-order statistic (conditional probability) was automatically computed, thereby allowing participants to predict the temporal order of shapes. Results of a single-shape test documented that lower-order statistics were retained during the extraction of higher-order statistics. These results suggest that observers automatically extract multiple statistics of temporal events that are suitable for efficient associative learning of new temporal features. Our visual experience consists almost entirely of spatiotemporal events created by observer movement through the visual array (through eye, head, and body movements) and/or by independent movements of objects with respect to the static environment.

Learning in many visual perceptual tasks has been shown to be specific to practiced stimuli, while new stimuli have to be learned from scratch. Here we demonstrate generalization using a novel paradigm in motion discrimination where learning has been previously shown to be specific. We trained subjects to discriminate directions of moving dots, and verified the previous results that learning does not transfer from a trained direction to a new one. However, by tracking the subjects' performance across time in the new direction, we found that their speed of learning doubled. Therefore, we found generalization in a task previously considered too difficult to generalize. We also replicated

The authors investigated how human adults encode and remember parts of multielement scenes composed of recursively embedded visual shape combinations. The authors found that shape combinations that are parts of larger configurations are less well remembered than shape combinations of the same kind that are not embedded. Combined with basic mechanisms of statistical learning, this embeddedness constraint enables the development of complex new features for acquiring internal representations efficiently without being computationally intractable. The resulting representations also encode parts and wholes by chunking the visual input into components according to the statistical coherence of their constituents. These results suggest that a bootstrapping approach of constrained statistical learning offers a unified framework for investigating the formation of different internal representations in pattern and scene perception.

Abbreviated title: Neural basis of the oblique effect Number of words in Abstract: 258 Number of text pages: 29 Number of figures: 15

Studies of perceptual learning consistently found that improvement is stimulus specific. These findings were interpreted as indicating an early cortical learning site. In line with this interpretation, we consider two alternative hypotheses: the `earliest modification' and the `output-level modification' assumptions, which respectively assume that learning occurs within the earliest representation which is selective for the trained stimuli, or at cortical levels receiving its output. We studied performance in a pop-out task using light bar distractor elements of one orientation, and a target element rotated by 30 (or 90). We tested the alternative hypotheses by examining pop-out learning through an initial training phase, a subsequent learning stage with swapped target and distractor orientations, and a final re-test with the originally trained stimuli. We found learning does not transfer across orientation swapping. However, following training with swapped orientations, a similar performance level is reached as with original orientations. That is, learning neither facilitates nor interferes to a substantial degree with subsequent performance with altered stimuli. Furthermore, this re-training does not hamper performance with the originally trained stimuli. If training changed the earliest orientation selective representation (specializing it for performance of the particular performed task) it would necessarily affect performance with swapped orientations, as well. The co-existence of similar asymptotes for apparently conflicting stimulus sets refutes the `earliest modification' hypothesis, supporting the alternative `output level modification' hypothesis. We conclude that secondary cortical processing levels use outputs from the earliest orientation representation to ...

Two experiments were conducted to determine the extent to which perceptual learning transfers between orientation and direction discrimination. Naive observers were trained to discriminate orientation differences between two single-line stimuli, and direction differences between two single-moving-dot stimuli. In the first experiment, observers practiced the orientation and direction tasks along orthogonal axes in the fronto-parallel plane. In the second experiment, a different group of observers practiced both tasks along a single axis. Perceptual learning was observed on both tasks in both experiments. Under the same-axis condition, the observers' orientation sensitivity was found to be significantly elevated after the direction training, indicating a transfer of learning from direction to orientation. There was no evidence of transfer in any other cases tested. In addition, the rate of learning on the orientation task was much higher than the rate on the direction task. The implicati...

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