Much research has examined preattentive vision: visual representation prior to the arrival of attention. Most vision research concerns attended visual stimuli; very little research has considered postattentive vision. What is the visual representation of a previously attended object once attention is deployed elsewhere? The authors argue that perceptual effects of attention vanish once attention is redeployed. Experiments 1-6 were visual search studies. In standard search, participants looked for a target item among distractor items. On each trial, a new search display was presented. These tasks were compared to repeated search tasks in which the search display was not changed. On successive trials, participants searched the same display for new targets. Results showed that if search was inefficient when participants searched a display the first time, it was inefficient when the same, unchanging display was searched the second, fifth, or 350th time. Experiments 7 and 8 made a similar point with a curve tracing paradigm. The results have implications for an understanding of scene perception, change detection, and the relationship of vision to memory.

No abstract

What is the orientation of an object? A simple line has an axis of orientation. That line, turned upside-down, is indistinguishable from the original line. Thus, the possible orientations of a line range from 0 to 180 degrees. Most objects, however, have an axis and a polarity. A polar object, turned upside-down, looks upside-down. Accordingly, the orientations of a polar object range from 0 to 360 degrees. A series of visual search experiments were run to determine if preattentive processes represent orientation in a 180 or a 360 degrees framework. Results suggest that preattentive orientation is represented in 180 degrees. Experiments 1 and 4 show that search for a target rotated 90 degrees from the distractors is more efficient than search for a target rotated 180 degrees from the distractors. Experiments 2, 3, and 5 use a variety of different stimuli to demonstrate that search for targets rotated 180 degrees from distractors is inefficient.

After surgery, the shaking limb episodes ceased for both patients. Postoperative single-photon emission computed tomographic scans for Patient 1 demonstrated increased cerebral blood flow in response to acetazolamide challenge. These data provide support for the concept that shaking limb TIAs are related to hemodynamic failure and that improvements in cerebral blood flow through conducting vessels can alleviate the condition.

After surgery, the shaking limb episodes ceased for both patients. Postoperative single-photon emission computed tomographic scans for Patient 1 demonstrated increased cerebral blood flow in response to acetazolamide challenge. These data provide support for the concept that shaking limb TIAs are related to hemodynamic failure and that improvements in cerebral blood flow through conducting vessels can alleviate the condition.