Mice with targeted genetic reduction of GABA(A) receptor alpha1 subunits display performance differences in Morris water maze tasks

Recent research has begun to demonstrate that specific subunits of GABA(A) receptors may be involved in the normal expression of specific behaviors. The present research used mice with GABA(A) receptors whose alpha1 subunits contained mutations of serine 270 to histidine and leucine 277 to alanine in the TM2 region. The purpose was an attempt to examine the possible role that this particular subunit may have in learning the spatial and nonspatial version of the Morris water maze task. Mutant animals, compared to controls, displayed elevated levels of pool circling in both the spatial task and the nonspatial task. These results suggested that normal performance of the spatial and nonspatial water maze tasks may be dependent upon a natural alpha1 subunit array.     

Equivalent testimonies as a touchstone of coherence measures

Over the past years, a number of probabilistic measures of coherence have been proposed. As shown in the paper, however, many of them do not conform to the intuitition that equivalent testimonies are highly coherent, regardless of their prior probability.     

The appraisal of facial beauty is rapid but not mandatory

Facial attractiveness is an important source of social affective information. Here, we studied the time course and task dependence of evaluating attractive faces from a viewer’s perspective. Event-related brain potentials (ERPs) were recorded while participants classified color portraits of unfamiliar persons according to gender and facial attractiveness. During attractiveness classification, enhanced ERP amplitudes for attractive and nonattractive faces relative to faces of intermediate attractiveness were found for an early component around 150 msec and for the late positive complex (LPC). Whereas LPC enhancement conforms to previous studies employing various types of affective stimuli, the finding of an early effect extends earlier research on rapid emotion processing to the dimension of facial attractiveness. Dipole source localization of this early ERP effect revealed a scalp distribution suggesting activation of posterior extrastriate areas. Importantly, attractiveness-related modulations of brain responses were only marginal during the gender decision task, arguing against the automaticity of attractiveness appraisal.     

Comparison of automated procedures for ARMA model identification

This article evaluates the performance of three automated proceduresfor ARMA modelidentification commonly available in current versions of SAS for Windows: MINIC, SCAN, and ESACF. Monte Carlo experiments with different model structures, parameter values, and sample sizes were used to compare the methods. On average, the procedures either correctly identified the simulated structures or selected parsimonious nearly equivalent mathematical representations in at least 60% of the trials conducted. For autoregressive models, MINIC achieved the best results. SCAN was superior to the other two procedures for mixed structures. For moving-average processes, ESACF obtained the most correct selections. For all three methods, model identification was less accurate for low dependency than for medium or high dependency processes. The effect of sample size was more pronounced for MINIC than for SCAN and ESACE SCAN and ESACF tended to select higher-order mixed structures in larger samples. These findings are confined to stationary nonseasonal time series.     

Coregistration of eye movements and EEG in natural reading: analyses and review

Brain-electric correlates of reading have traditionally been studied with word-by-word presentation, a condition that eliminates important aspects of the normal reading process and precludes direct comparisons between neural activity and oculomotor behavior. In the present study, we investigated effects of word predictability on eye movements (EM) and fixation-related brain potentials (FRPs) during natural sentence reading. Electroencephalogram (EEG) and EM (via video-based eye tracking) were recorded simultaneously while subjects read heterogeneous German sentences, moving their eyes freely over the text. FRPs were time-locked to first-pass reading fixations and analyzed according to the cloze probability of the currently fixated word. We replicated robust effects of word predictability on EMs and the N400 component in FRPs. The data were then used to model the relation among fixation duration, gaze duration, and N400 amplitude, and to trace the time course of EEG effects relative to effects in EM behavior. In an extended Methodological Discussion section, we review 4 technical and data-analytical problems that need to be addressed when FRPs are recorded in free-viewing situations (such as reading, visual search, or scene perception) and propose solutions. Results suggest that EEG recordings during normal vision are feasible and useful to consolidate findings from EEG and eye-tracking studies.     

Multiple contributions to priming effects for familiar faces: analyses with backward masking and event-related potentials

The model of face recognition by Bruce and Young postulates a pool of structural representations for familiar faces in long-term memory, so-called face recognition units (FRUs). Event-related brain potentials show early repetition priming effects for familiar faces around 250-300 ms [N250r or early repetition effect (ERE)], which are thought to reflect the activation of these FRUs. However, small N250r effects are also seen for unfamiliar faces suggesting that priming of perceptual codes (i.e., pictorial and structural codes) also contributes to early repetition effects. Using a face-familiarity task in Experiment 1, we aimed to eliminate these perceptual contributions to face priming by backward masking the prime face with a different, unfamiliar face. As expected, a repetition priming effect appeared only for familiar faces. Experiment 2 used a semantic-decision task and compared the effects of different kinds of masks that interfered with either pictorial codes or with pictorial and structural codes. Our findings indicate that both structural codes and memory representations contribute to the N250r and that unfamiliar-face masks interfere only with structural codes. Face-masks may therefore provide a useful tool to extract the pure contributions of memory representations (i.e., FRUs) to repetition priming.     

Subitizing reflects visuo-spatial object individuation capacity

Subitizing is the immediate apprehension of the exact number of items in small sets. Despite more than a 100 years of research around this phenomenon, its nature and origin are still unknown. One view posits that it reflects a number estimation process common for small and large sets, which precision decreases as the number of items increases, according to Weber’s law. Another view proposes that it reflects a non-numerical mechanism of visual indexing of multiple objects in parallel that is limited in capacity. In a previous research we have gathered evidence against the Weberian estimation hypothesis. Here we provide first direct evidence for the alternative object indexing hypothesis, and show that subitizing reflects a domain general mechanism shared with other tasks that require multiple object individuation.