Imagine yourself at a party with someone that you have a crush on or are even in love with. You seem to be constantly aware of where that person is, and your gaze is repeatedly drawn toward the dashing red shirt or dress that he or she is wearing or to their shining black hair, in such fine contrast to their paler face, despite your best efforts to not look too eager. This person is an example of a stimulus that is the focus of your attention and matters very much to you. Recent research has unveiled how our attention and gaze seem to be automatically drawn toward those features that we have recently attended to and are important to us, such as the red dress or dark hair of our object of desire. Such priming appears to have a very strong effect on what grabs our attention. Recent research on priming in visual search tasks suggests that we possess a primitive memory system drawing our attention to features or objects that we have recently attended to and are important to our goals or to the task that we are performing. We seem to have little or no voluntary control over the workings of this memory system. We review a large body of neurophysiological and neuropsychological evidence with regard to such priming that suggests that activity changes in the neural mechanisms devoted to the analysis of the particular stimuli for which priming effects are seen are the source of the observed priming effects and that these activity modulations occur at a number of different levels of the visual hierarchy. Basic Characteristics of PrimingSince the pioneering studies of Maljkovic and Nakayama (1994, 1996) and Treisman (1992), a large number of studies have addressed priming effects in visual search. This research has shown that our perception is heavily influenced by what we have seen in the past. As we search for a target of, say, a particular color, detection or discrimination of that target or features of that target (such as its shape, color, or location) becomes easier if we are familiar with it or if we have seen it or acted upon it before. This has been widely investigated by means of controlled lab experiments in which the effects of previously presented displays on performance in the present have been investigated. Such effects, called perceptual What we have recently seen and attended to strongly influences how we subsequently allocate visual attention. A clear example is how repeated presentation of an object's features or location in visual search tasks facilitates subsequent detection or identification of that item, a phenomenon known as priming. Here, we review a large body of results from priming studies that suggest that a short-term implicit memory system guides our attention to recently viewed items. The nature of this memory system and the processing level at which visual priming occurs are still debated. Priming might be due to activity modulations of low-level areas coding simple stimulus characteristics or to higher level episodic memory representations of whole objects or visual scenes. Indeed, recent ...

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Presentation of supraliminal or subliminal visual stimuli that can (or cannot) be detected or identified can improve the probability of the same stimulus being detected over a subsequent period of seconds, hours or longer. The locus and nature of this perceptual priming effect was examined, using suprathreshold stimuli, in subjects who received repetitive pulse transcranial magnetic stimulation over the posterior occipital cortex, the extrastriate motion area V5/MT or the right posterior parietal cortex during the intertrial interval of a visual motion direction discrimination task. Perceptual priming observed in a control condition was abolished when area V5/MT was stimulated but was not affected by magnetic stimulation over striate or parietal sites. The effect of transcranial magnetic stimulation (TMS) on priming was specific to site (V5/MT) and to task - colour priming was unaffected by TMS over V5/MT. The results parallel, in the motion domain, recent demonstrations of the importance of macaque areas V4 and TEO for priming in the colour and form domains.

We investigated whether lateral masking in the near-periphery, due to inhibitory lateral interactions at an early level of central visual processing, could be weakened by perceptual learning and whether learning transferred to an untrained, higher-level lateral masking known as crowding. The trained task was contrast detection of a Gabor target presented in the near periphery (4°) in the presence of co-oriented and co-aligned high contrast Gabor flankers, which featured different target-to-flankers separations along the vertical axis that varied from 2λ to 8λ. We found both suppressive and facilitatory lateral interactions at target-to-flankers distances (2λ - 4λ and 8λ, respectively) that were larger than those found in the fovea. Training reduces suppression but does not increase facilitation. Most importantly, we found that learning reduces crowding and improves contrast sensitivity, but has no effect on visual acuity (VA). These results suggest a different pattern of connectivity in the periphery with respect to the fovea as well as a different modulation of this connectivity via perceptual learning that not only reduces low-level lateral masking but also reduces crowding. These results have important implications for the rehabilitation of low-vision patients who must use peripheral vision to perform tasks, such as reading and refined figure-ground segmentation, which normal sighted subjects perform in the fovea.

The motion after-effect is a robust illusion of visual motion resulting from exposure to a moving pattern. There is a widely accepted explanation of it in terms of changes in the response of cortical direction-selective neurons. Research has distinguished several variants of the effect. Converging recent evidence from different experimental techniques (psychophysics, single-unit recording, brain imaging, transcranial magnetic stimulation, and evoked potentials) reveals that adaptation is not confined to one or even two cortical areas, but involves up to five different sites, reflecting the multiple levels of processing involved in visual motion analysis. A tentative motion processing framework is described, based on motion after-effect research. Recent ideas on the function of adaptation see it as a form of gain control that maximises the efficiency of information transmission.