Comparing neural correlates of configural processing in faces and objects:An ERP study of the thatcher illusion

In the Thatcher illusion, a face with inverted eyes and mouth looks abnormal when upright but not when inverted. Behavioral studies have shown that thatcherization of an upright face disrupts perceptual processing of the local configuration. We recorded high-density EEG from normal observers to study ERP correlates of the illusion during the perception of faces and nonface objects, to determine whether inversion and thatcherization affect similar neural mechanisms. Observers viewed faces and houses in four conditions (upright vs. inverted, and normal vs. thatcherized) while detecting an oddball category (chairs). Thatcherization delayed the N170 component over occipito-temporal cortex to faces, but not to houses. This modulation matched the illusion as it was larger for upright than inverted faces. The P1 over medial occipital regions was delayed by face inversion but unaffected by thatcherization. Finally, face thatcherization delayed P2 over occipito-temporal but not over parietal regions, while inversion affected P2 across categories. All effects involving thatcherization were face-specific. These results indicate that effects of face inversion and feature inversion (in thatcherized faces) can be distinguished on a functional as well as neural level, and that they affect configural processing of faces in different time windows. © 2006 Elsevier Inc.

Topography of the visual evoked magnetic response and hemispherical specialization

The visual evoked magnetic response CIIm component to a pattern onset stimulus presented half field produced a consistent scalp topography in 15 normal subjects. The major response was seen over the contralateral hemisphere, suggesting a dipole with current flowing away from the medial surface of the brain. Full field responses were more unpredictable. The reponses of five subjects were studied to the onset of a full, left half and right half checkerboard stimuli of 38 x 27 min arc checks appearing for 200 ms. In two subjects the full field CIIm topography was consistent with that of the mathematical summation of their relevant half field distribution. The remaining subjects had unpredictable full field topographies, showing little or no relationship to their half or summated half fields. In each of these subjects, a distribution matching that of the summated half field CIIm distribution appears at an earlier latency than that of the predominant full field waveform peak. By examining the topography of the full and half field responses at 5 ms intervals along the waveform for one such subject, the CIIm topography of the right hemisphere develops 10 ms before that of the left hemisphere, and is replaced by the following CIIIm component 20 ms earlier. Hence, the large peak seen in full field results from a combination of the CIIm component of the left hemisphere plus that of the CIIIm from the right. The earlier peak results from the CIIm generated in both hemispheres, at a latency where both show similar amplitudes. As the relative amplitudes of these two peaks alter with check and field size, topographic studies would be required for accurate CIIm identification. In addition. the CIIm-CIIIm complex lasts for 80 ms in the right hemisphere and 135 ms in the left, suggesting hemispherical apecialization in the visual processing of the pattern onset response.

Influence of downstream processing on the breakage of whey protein precipitates

Whey proteins may be fractionated by isoelectric precipitation followed by centrifugal recovery of the precipitate phase. Transport and processing of protein precipitates may alter the precipitate particle properties, which may affect how they behave in subsequent processes. For example, the transport of precipitate solution through pumps, pipes and valves and into a centrifugal separator may cause changes in particle size and density, which may affect the performance of the separator. This work investigates the effect of fluid flow intensity, flow geometry and exposure time on the breakage of whey protein precipitates: Computational fluid dynamics (CFD) was used to quantify the flow intensity in different geometries. Flow geometry can have a critical impact on particle breakage. Sharp geometrical transitions induce large increases in turbulence that can result in substantial particle breakage. As protein precipitate particles break, they tend to form denser more compact structures. The reduction in particle size and increase in compaction is due to breakage. This makes the particles become more resistant to further breakage as particle compactness increases. The effect of flow intensity on particle breakage is coupled to exposure time, with greater exposure time producing more breakage. However, it is expected that the particles will attain an equilibrium particle size and density after prolonged exposure in a constant flow field where no further breakage will occur with exposure time. © 2005 Institution of Chemical Engineers.