Many studies have found that the P50 sensory gating ratio in a paired click task is smaller in normal control subjects than in patients with schizophrenia, indicating more effective sensory gating. However, a wide range of gating ratios has been reported in the literature for both groups. The purpose of this study was to compile these findings and to compare reported P50 gating ratios in controls and patients with schizophrenia. Current data collected from individual controls in eight studies from the University of California, Irvine (UCI), Indiana University (IU), and Yale University also are reported. The IU, UCI, and Yale data showed that approximately 40% of controls had P50 ratios within 1 S.D. below the mean of means for patients with schizophrenia. The meta-analysis rejected the null hypothesis that all studies showed no effect. The meta-analysis also showed that the differences were not the same across all studies. The mean ratios in 45 of the 46 group comparisons were smaller for controls than for patients, and the observed difference in means was significant for 35 of those studies. Reported gating ratios for controls from two laboratories whose findings were reported in the literature differed from all the other control groups. Variables affecting the gating ratio included band pass filter setting, rules regarding the inclusion of P30, sex, and age. Standards of P50 collection and measurement would help determine whether the gating ratio can be sufficiently reliable to be labeled an endophenotype, and suggestions are made toward this goal.

Studies of task switching demonstrate that task switches are associated with response costs and that these costs are reduced when a cue is presented in advance of a switch. The present study examined cortical event-related potential correlates of task switching and switch costs in 39 participants during a cued match/mismatch discrimination task. Compared with non-switch trials, switch trials were associated with a larger cue-related, anticipatory P3b-like waveform. Switch trials were also associated with smaller target-related, stimulus-dependent P2 and P3-like components. Moreover, the switch-related amplitude variability in the P3b to the cue and the P2 to the target were associated with unique components of the residual switch costs. The results support an integrated model of task switching with complementary yet distinct roles for anticipatory and stimulus-dependent processes in task switching and switch costs.

EEG studies of wakeful rest have shown that there are brief periods in which global electrical brain activity on the scalp remains semi-stable (so-called microstates). Topographical analyses of this activity have revealed that much of the variance is explained by four distinct microstates that occur in a repetitive sequence. A recent fMRI study showed that these four microstates correlated with four known functional systems, each of which is activated by specific cognitive functions and sensory inputs. The present study used high density EEG to examine the degree to which spatial and temporal properties of microstates may be altered by manipulating cognitive task (a serial subtraction task vs. wakeful rest) and the availability of visual information (eyes open vs. eyes closed conditions). The hypothesis was that parameters of microstate D would be altered during the serial subtraction task because it is correlated with regions that are part of the dorsal attention functional system. It was also expected that the sequence of microstates would preferentially transition from all other microstates to microstate D during the task as compared to rest. Finally, it was hypothesized that the eyes open condition would significantly increase one or more microstate parameters associated with microstate B, which is associated with the visual system. Topographical analyses indicated that the duration, coverage, and occurrence of microstate D were significantly higher during the cognitive task compared to wakeful rest; in addition, microstate C, which is associated with regions that are part of the default mode and cognitive control systems, was very sensitive to the task manipulation, showing significantly decreased duration, coverage, and occurrence during the task condition compared to rest. Moreover, microstate B was altered by manipulations of visual input, with increased occurrence and coverage in the eyes open condition. In addition, during the eyes open condition microstates A and D had significantly shorter durations, while C had increased occurrence. Microstate D had decreased coverage in the eyes open condition. Finally, at least 15 microstates (identified via k-means clustering) were required to explain a similar amount of variance of EEG activity as previously published values. These results support important aspects of our hypotheses and demonstrate that cognitive manipulation of microstates is possible, but the relationships between microstates and their corresponding functional systems are complex. Moreover, there may be more than four primary microstates.

The associative learning effects called blocking and highlighting have previously been explained by covert learned attention, but evidence for learned attention has been indirect, via models of response choice. The present research reports results from eye tracking consistent with the attentional hypothesis: Gaze duration is diminished for blocked cues and augmented for highlighted cues. If degree of attentional learning varies across individuals but is relatively stable within individuals, then the magnitude of blocking and highlighting should covary across individuals. This predicted correlation is obtained for both choice and eye gaze. A connectionist model that implements attentional learning is shown to fit the data and account for individual differences by variation in its attentional parameters.Keywords: blocking, highlighting, learned attention, eye tracking, individual differencesThe phenomenon of blocking has become a touchstone for theories of learning. Reported initially by Kamin (1968Kamin ( , 1969 and found thereafter in numerous species and procedures, the phenomenon forced a revolution in theories of learning. In the blocking procedure, a person initially learns to predict an outcome from a single cue. Subsequently, the cue is always accompanied by a second cue, still leading to the same outcome. People tend not to learn a strong association between the second cue and the outcome; that is, previous learning about the first cue has blocked learning about the second cue. This blocking challenges some theories of learning because the second cue has co-occurred with the outcome quite often and their association should be learned.A complementary phenomenon called highlighting suggests augmented learning about a cue, in contrast to the diminished learning in blocking (Kruschke, 2003a). This phenomenon is extremely challenging to learning theories, even those that were created to account for blocking (such as the Rescorla-Wagner model, which will be explained below). In a highlighting procedure, participants initially learn that a pair of cues leads to an outcome. Later, participants learn that one of those cues, paired with a different cue, leads to a different outcome. The result is that the association from the distinctive cue to the later-learned outcome is apparently very strong; that is, learning about the distinctive cue has been highlighted.To our knowledge, only attentional theory (Kruschke, 2003a) explains both highlighting and blocking. According to this approach, highlighting occurs because people have learned to attend to the distinctive cue for the new outcome. Blocking occurs, at least in part but not fully, because people have learned to ignore the redundant cue. The attentional theory will be explained in more detail later; for now we wish to emphasize that the attention posited in this theory is a theoretical construct referring to a covert aspect of cognition. The formal theory simply states that more strongly attended cues are multiplied by a larger factor in responding and learning....