Expectancy of line segment orientation

Attention as a Unitary Concept

In this paper, I discuss attention in terms of selecting visual information and acting on it. Selection has been taken as a bedrock concept in attention research since James (1890). Selective attention guides action by privileging some things at the expense of others. I formalize this notion with models which capture the relationship between input and output under the control of spatial and temporal attention, by attenuating or discarding certain inputs and by weighing energetic costs, speed, and accuracy in meeting pre-chosen goals. Examples are given from everyday visually guided actions, and from modeling data obtained from visual searches through temporal and spatial arrays and related research. The relation between selection, as defined here, and other forms of attention is discussed at the end.

Attention and Signal Detection

In this paper, I first review signal detection theory (SDT) approaches to perception, and then discuss why it is thought that SDT theory implies that increasing attention improves performance. Our experiments have shown, however, that this is not necessarily true. Subjects had either focused attention on two of four possible locations in the visual field, or diffused attention to all four locations. The stimuli (offset letters), locations, conditions, and tasks were all known in advance, responses were forced-choice, subjects were properly instructed and motivated, and instructions were always valid—conditions which should optimize signal detection. Relative to diffusing attention, focusing attention indeed benefitted discrimination of forward from backward pointing Es. However, focusing made it harder to identify a randomly chosen one of 20 letters. That focusing can either aid or disrupt performance, even when cues are valid and conditions are idealized, is surprising, but it can also be explained by SDT, as shown here. These results warn the experimental researcher not to confuse focusing attention with enhancing performance, and warn the modeler not to assume that SDT is unequivocal.

Interference between smooth pursuit and color working memory

Spatial working memory (WM) and spatial attention are closely related, but the relationship between non-spatial WM and spatial attention still remains unclear. The present study aimed to investigate the interaction between color WM and smooth pursuit eye movements. A modified delayed-match-to-sample paradigm (DMS) was applied with 2 or 4 items presented in each visual field. Subjects memorized the colors of items in the cued visual field and smoothly moved eyes towards or away from memorized items during retention interval despite that the colored items were no longer visible. The WM performance decreased with higher load in general. More importantly, the WM performance was better when subjects pursued towards rather than away from the cued visual field. Meanwhile, the pursuit gain decreased with higher load and demonstrated a higher result when pursuing away from the cued visual field. These results indicated that spatial attention, guiding attention to the memorized items, benefits color WM. Therefore, we propose that a competition for attention resources exists between color WM and smooth pursuit eye movements.

Attention directed by expectations enhances receptive fields in cortical area MT

Expectations, especially those formed on the basis of extensive training, can substantially enhance visual performance. However, it is not clear that the physiological mechanisms underlying this enhancement are identical to those examined by experiments in which attention is directed by explicit instructions rather than strong expectations. To study the changes in visual representations associated with strong expectations, we trained animals to detect a brief motion pulse that was embedded in noise. Because the nature of the pulse and the statistics of its appearance were well known to the animals, they formed strong expectations which determined their behavioral performance. We used white-noise methods to infer the receptive field structure of single neurons in area MT while they were performing this task. Incorporating non-linearities, we compared receptive fields during periods of time when the animals were expecting the motion pulse with periods of time when they were not. We found receptive field changes consistent with an increased reliability in signaling pulse occurrence. Moreover, these changes were not consistent with a simple gain modulation. The results suggest that strong expectations can create very specific changes in the visual representations at a cellular level to enhance performance.

The role of attention in binding shape to color

Pictures of easily-identifiable objects with novel colors (e.g. a blue frog) or of forms with arbitrary colors (e.g. a green triangle) were presented briefly at 10.6 degrees eccentricity. Stimuli had strong outlines and vivid fill colors (red, green, yellow, blue, or purple). The same pictures were repeated once in each block of 30 trials for 6, 9, or 12 blocks, and recognition was probed after each block. Shapes were acquired quickly, within 3-4 blocks, whether attention was focused on the pictures or split to a demanding foveal task. Color-shape acquisition was also fast with focused attention, but stabilized at a low level with split attention. Delaying the foveal task restored color-shape acquisition. We suggest that attention facilitates the creation and maintenance of novel color-shape bindings in the visual periphery; without attention, binding is less effective.

Expectancy effects on spatial frequency processing

We explored top-down modulation of spatial frequency (SF) processing. When auditory pre-cueing directed observers' attention to one of two 4-octaves (SF) apart plaid components observers tended to perceive the cued component, suggesting selective attention to the SF channel they expected to carry task relevant information. In agreement, pre-cueing had no effect with components often processed by the same channel (0.5-octaves apart). Further, effects of expectancy were greater than of uncertainty and were SF tuned. Combined our findings suggest top-down modulation of early, cortical, SF processing. We argue this could similarly explain the previously reported influences of categorisation on SF processing.

Uncertainty, attentional capacity and chromatic mechanisms in visual search

Two general questions were investigated using a visual search task. First, we asked whether effects of target uncertainty on reaction time varied with the discriminability of the target and distractors. Second, a higher order chromatic mechanism model was tested against a flexible model in which the signals in cardinal color-opponent mechanisms are combined through an attentional process. The models were tested by measuring the effects of target uncertainty on search time. A regression analysis indicated that the magnitude of the uncertainty effect was approximately constant in logarithmic units as a function of the chromatic difference between the target and distractors. The constant magnitude of the uncertainty effect suggested that an attentional capacity limit was exceeded when observers were required to monitor several chromatic mechanisms at several locations. The results of experiments 3 and 4 suggested that search for chromatic targets among distractors was mediated by diagonally tuned higher order chromatic mechanisms, rather than by signals in cardinal color-opponent mechanisms that were combined through an attentional mechanism.

Spatial attention improves performance in spatial resolution tasks

This study used peripheral precueing to explore the effect of covert transient attention on performance in spatial resolution tasks. Experiments 1 (Landolt-square) and 2 ('broken-line') measured gap resolution and Experiment 3 measured vernier resolution. In all three tasks the target was presented alone in a large number of possible locations, ranging from 1.5-6 degrees of eccentricity in the vertical or horizontal axes. The precue indicated the target location but did not convey information regarding the correct response. Performance decreased as the gap size or the vernier offset size decreased and as target eccentricity increased. Precueing improved performance in terms of RT and accuracy in all three tasks; the eccentricity effect decreased in the cued trials of the gap resolution tasks. These findings support the idea that the performance improvement at attended locations results, to some extent, from an enhanced spatial resolution at the cued location, and not just from distractor exclusion, diminished uncertainty, or decisional factors.