Retention of attended and unattended auditorily and visually presented material

In the first of two experiments investigating focussed attention, sets of four pairs of digits were dichotically presented to subjects who were instructed to attend to digits arriving in either the left or the right ear. Following presentation, two different report orders were used: attended followed by unattended, and unattended followed by attended. It was found that unattended items did not suffer from being recalled second rather than first. The serial position curve for unattended items was U-shaped. These results were interpreted as evidence that unattended items are not retained in a limited-capacity auditory buffer with a fast rate of loss. The experiment was repeated using visually presented pairs of letters. A similar pattern of results was obtained, consistent with the hypothesis that unattended items are recalled from a store with a large capacity and a very slow rate of loss.     

Visual texture perception and Fourier analysis

The relationship between the Fourier spectra of visual textures (represented by four hypothetical visual channels sensitive to spatial frequencies) and the perceptual appearance of the textures was investigated. Thirty textures were synthesized by combining various spatial frequencies of different amplitudes. Twenty subjects grouped the textures into 2, 3, 4, and 5 groups based on the similarity of their appearance. The groupings were analyzed by means of linear discriminant analysis using the activity of the four channels as predictor variables. The groupings were also examined by multidimensional scaling, and the resulting stimulus configuration was canonically correlated with the channel activity. The results of both analyses indicate a strong relationship between the perceptual appearance of the textures and their Fourier spectra. These findings suport a multiple-channel spatial-frequency model of perception.     

The quantitative measure of pattern representation in images using orientation-specific color aftereffects

A quantitative method is developed for assessing the quality of pattern information in imagery, using the magnitude of color aftereffects as an objective index. Subjects were given instructions to project imagined bar patterns of particular width and orientation onto adapting color fields, in such a manner as to simulate standard conditions for establishing the McCollough effect. Our control procedures indicate that the resulting orientation-specific complementary color aftereffects cannot be attributed to the conditioning of particular directions of eye scanning movements to color processing during adaptation, or to other possible sources of experimental bias. Furthermore, subjects who rated themselves prior to the adaptation procedure as having relatively vivid imagery showed significantly larger aftereffects than those who reported having relatively low imagery. These results not only provide an important confirmation of our earlier finding that imagination can replace physical pattern information in the formation of basic color-feature associations in the human visual system, but also demonstrate that these aftereffects can provide a practical measure of the fidelity of pattern representation in visual images.     

Visual discrimination of texture

Julesz (1975) proposed a theory of texture discrimination, based on an order statistics principle, which states that no two textures can be perceptually discriminated if they have identical second-order statistics. The experiments reported here demonstrate that this principle is not adequate to predict visual texture discriminability. Both letter and dot micropatterns were used to create texture pairs that either differed or were identical with respect to secondorder statistics. The subject’s task was to decide which quadrant of an array contained a disparate texture. In Experiments 1, 2, and 3, when controlling for spatial overlap, texture pairs having identical second-order statistics were discriminated more quickly than similar texture pairs having different second-order statistics, in contradiction to the principle. Although a significant effect in the direction predicted by the order statistics principle was found in Experiment 4 for texture pairs created from the dot micropatterns, other factors, such as spatial overlap, border differences, and goodness of pattern, must also be considered in predicting texture discriminability.     

Attention to words in different modalities: Four-channel presentation with physical and semantic selection

Theoretical controversy surrounds the issue of whether central processing capacity is unitary and general or whether different types of processing capacity may be distinguished. Three bisensory experiments investigated the selection of words by physical and semantic attributes. It was found that recall was superior following bimodal (auditory and visual) rather than unimodal (auditory or visual) presentation. Furthermore, the difference between bimodal and unimodal recall was greater when the words were physically selected than when they were semantically selected. The results provide evidence that the availability of different types of processing capacity is dependent upon the mode of presentation of material and its required type of analysis.     

A SUPERVISORY STRATEGY TO IMPROVE WORK PERFORMANCE FOR LOWER FUNCTIONING RETARDED CLIENTS IN A SHELTERED WORKSHOP

A multiple component strategy was investigated for aiding staff responsible for supervising production of lower functioning retarded clients on contract tasks in an institution-based sheltered workshop. The strategy was assessed in a combined multi-element, multiple baseline across groups design with a reversal component. Production performance increased during the production supervisory strategy with all 16 clients, with the range of increase varying from a few percentage points to 150% of baseline production. Both the clients and staff (responsible for conducting the research) preferred working under experimental conditions rather than under baseline conditions which approximated those found in “typical” sheltered workshops.