Texture variations suppress suprathreshold brightness and colour variations

Discriminating material changes from illumination changes is a key function of early vision. Luminance cues are ambiguous in this regard, but can be disambiguated by co-incident changes in colour and texture. Thus, colour and texture are likely to be given greater prominence than luminance for object segmentation, and better segmentation should in turn produce stronger grouping. We sought to measure the relative strengths of combined luminance, colour and texture contrast using a suprathreshhold, psychophysical grouping task. Stimuli comprised diagonal grids of circular patches bordered by a thin black line and contained combinations of luminance decrements with either violet, red, or texture increments. There were two tasks. In the Separate task the different cues were presented separately in a two-interval design, and participants indicated which interval contained the stronger orientation structure. In the Combined task the cues were combined to produce competing orientation structure in a single image. Participants had to indicate which orientation, and therefore which cue was dominant. Thus we established the relative grouping strength of each cue pair presented separately, and compared this to their relative grouping strength when combined. In this way we observed suprathreshold interactions between cues and were able to assess cue dominance at ecologically relevant signal levels. Participants required significantly more luminance and colour compared to texture contrast in the Combined compared to Separate conditions (contrast ratios differed by about 0.1 log units), showing that suprathreshold texture dominates colour and luminance when the different cues are presented in combination

Structure and resistivity of bismuth thin films deposited by pulsed DC sputtering

The final publication is available at Springer via http://dx.doi.org/10.1007/s00339-015-9337-3Bismuth thin films have been deposited using pulsed DC magnetron sputter deposition under four deposition conditions, combining powers of 50 and 100 W and argon gas pressures, 2 and 10 mTorr. Estimated deposition rates were between 0.08 and 3.5 nm s−1. The films were examined using scanning electron microscopy, cross-sectioning using a focussed ion beam (FIB), X-ray diffraction and sheet resistance and Hall effect measurement. Room temperature deposition gave a predominant orientational texture of (111) rhombohedral. However, higher film thickness, low sputtering power, high sputtering gas pressure and deposition onto a heated substrate above 125 °C increase the fraction of (110) orientation. FIB cross-sectioning indicates that films deposited at room temperature have an irregular crystalline structure with voids, but those grown at 160 °C are denser with a better polycrystalline structure. Transport measurements indicate a dominance of conduction by electrons, with films deposited at room temperature having high sheet resistance, low sheet resistance being favoured by low sputtering pressure. Deposition at higher temperatures improves the conductivity but increases the Hall coefficient

Complete sparing of high-contrast color input to motion perception in cortical color blindness

It is widely held that color and motion are processed by separate parallel pathways in the visual system, but this view is difficult to reconcile with the fact that motion can be detected in equiluminant stimuli that are defined by color alone. To examine the relationship between color and motion, we tested three patients who had lost their color vision following cortical damage (central achromatopsia). Despite their profound loss in the subjective experience of color and their inability to detect the motion of faint colors, all three subjects showed surprisingly strong responses to high-contrast, moving color stimuli — equal in all respects to the performance of subjects with normal color vision. The pathway from opponent-color detectors in the retina to the motion analysis areas must therefore be independent of the damaged color centers in the occipitotemporal area. It is probably also independent of the motion analysis area MT/V5, because the contribution of color to motion detection in these patients is much stronger than the color response of monkey area MT