We assume a rather specific function for alpha not only with respect to the type of cognitive processes but also with respect to physiology. Tenofovir molecular weight With respect to physiology one important

aspect is that alpha operates to inhibit task irrelevant neural structures and thereby helps to establish a more focused access to the KS. There may be different kinds of attentional processes comprising e.g., also those which rely on excitatory processes only. In addition, there may be different kinds of attention, related to different cognitive processing modes, such as a sustained focus on the encoding of new or alerting information. We consider alpha a specific kind of attention that is related to inhibitory control processes of the KS. The next section is a selective review about variables that typically modulate P1 amplitude and/or latency. The most important examples are (1) spatial attention, (2) reflexive attention, (3) object based attention, (4) target properties investigated in search paradigms, and (5) perceptual features. The aim of this brief review is to provide evidence for the

second assumption stating that the P1 amplitude reflects early categorization processes during access to the KS, which are based on the analysis of global stimulus properties. The spatial location of a relevant stimulus or object may be considered an important variable that influences early stages of visual processing and access to the KS. For the investigation of spatial attention, at least three types of paradigms can be distinguished. The first DNA Damage inhibitor two investigate top–down controlled spatial selection processes. As illustrated in Fig. 1A, type 1 paradigms are designed to direct attention to a specific location – usually to the left or right hemifield – over a run (block) of trials simply by instructing subjects to do so. Type 2 paradigms use a cue to direct attention to a specific location on a trial per trial basis. Type 3 paradigms are used

to study Glutathione peroxidase reflexive attention, either using a cue or not. Convergent evidence from type 1 and 2 paradigms indicates that stimuli flashed at an attended location elicit a larger P1 than stimuli flashed at unattended locations (e.g., Heinze et al., 1994, Heinze and Mangun, 1995, Mangun et al., 1997 and Mangun and Buck, 1998 for reviews cf. Mangun, 2003, Hillyard et al., 1998 and Hillyard and Anllo-Vento, 1998). As a first example, let us consider the findings from a type 1 paradigm (attend left vs. right hemifield) used in a study by Mangun et al. (2001). Stimuli were gratings of vertically oriented black and white stripes and were presented for 100 ms. Targets were slightly shorter than standards and appeared in 25% of all trials. All stimuli were randomly presented to the left or right hemifield. Subjects were instructed to respond to a target in the attended hemifield only. The results for standard stimuli are depicted in Fig.