Visual evoked cortical responses and selective dioptic masking with pattern flashes of different spatial frequencies

Human cortical visually evoked responses (VERs) to pairs of stimuli presented in rapid succession were investigated in an attempt to assess the electrophysiological nature of temporal visual processing as a function of the spatial frequency of the stimuli involved. Four stimuli, all of which were of an equal mean luminance level, consisted of a diffuse flash and square checkerboard patterns of three spatial frequencies: 0.5, 1.0, and 4.0 cycles/degree (check-sizes subtending 60, 30, and 7.5 min of arc visual angle). Stimuli were presented both singly and in all 16 possible pairwise combinations with a 40 msec interflash interval interposed between the pairs. Both the psychophysical reports and the VERs to the various stimulus configurations were analyzed in order to test whether the existence of visual information channels selectively tuned to a specific range of spatial frequencies would be revealed in terms of selective masking effects among the various stimulus combinations. Analysis of the VER data was based primarily on the magnitude of variability of the VERs, resulting from variations in the pattern stimulation from the first or second flash. The variability measure indicated the degree to which stimulus pattern processing of one flash of the pair was impaired by the nature of pattern in the preceding or following flash (forward and backward masking effects respectively)

Psychophysical performance, contingent negative variations, visually evoked cortical potentials, and selective attention : a behavioral and neurophysiological assessment of learning disabilities in children

The present experiment was designed to assess whether any attentional, perceptual, or neurophysiological differences exist between children classified as reading disabled and normal. A visual discrimination task was employed, which required attentional and perceptual capabilities; wherein the children were required to selectively attend and respond to one stimulus of a pair and to ignore the other stimulus. Four pairs of stimuli (colors, line orientations, letters, and words) of different levels of complexity were discriminated in order to provide clues as to the possible level of neural processing accounting for the reading disability. The children's ability to attend and to discriminate each stimulus in a pair was measured both behaviorally by psychophysical measures of response accuracy (d’) and reaction time, and also electrophysiologically by visually evoked cortical potentials (VEPs) and contingent negative variations (CNVs). A secondary purpose of the study was to examine whether the learning disability was restricted to one sensory modality. Children who were diagnosed as having either a visual or an auditory disability participated in the experiment so as to determine whether only the visual learning disability children would have difficulty with the visual discrimination task. Therefore, three groups of subjects, matched for age, sex, and IQ, were employed: normal controls (NC), visual learning disabled (VLD), and auditory learning disabled (ALD)

Where Brain, Body and World Collide

The production cross section of electrons from semileptonic decays of beauty hadrons was measured at mid-rapidity (|y| < 0.8) in the transverse momentum range 1 < pt < 8 Gev/c with the ALICE experiment at the CERN LHC in pp collisions at a center of mass energy sqrt{s} = 7 TeV using an integrated luminosity of 2.2 nb^{-1}. Electrons from beauty hadron decays were selected based on the displacement of the decay vertex from the collision vertex. A perturbative QCD calculation agrees with the measurement within uncertainties. The data were extrapolated to the full phase space to determine the total cross section for the production of beauty quark-antiquark pairs