Observation of the naturally-occurring accommodative response of a highly visual teleost species provides the opportunity to study its stimulus-response accuracy. A video recording system, linked to a computer digitizing program, was used to measure accommodative changes in lens position in the oscar, Astronotus ocellatus, in response to known food stimuli. The largest lens deviations occurred ...

Two line gratings abutting each other with a phase shift of half a cycle elicit the perception of an illusory line running orthogonally between the two sets of grating lines. We found that rating strength increases with increasing number of lines, line length, and phase angle. In contrast, rating strength decreases with increasing spacing of lines, lateral misalignment, rotation of one grating ...

The detectability of a 9·0 c/deg sinusoidal grating was measured against various backgrounds: A blank field, a 3·0 c/deg grating and a 1·8 c/deg grating. Detection of the 9·0 c/deg grating was facilitated by suprathreshold 3·0 c/deg grating backgrounds (3·0 and 9·0 c/deg are first and third harmonics), but was not facilitated by 1·8 c/deg grating backgrounds (first and fifth harmonics). The res...

The b1icrowave Anisotropy Probe (MAP) launched successfully on June 30, 2001 and is presently in a Lissajous orbit about the Sun-Earth libration point L2. To avoid Earth shadows at L2, the Sun-EarthVehicle (SEV) angle of MAP has to be-greater than 0.5 deg for an extended mission of four years. An equation is derived for the SEV angle in terms of the phase angle, frequencies and amplitudes of th...

The aim of this study was to investigate the spatial-frequency bandwidth of perceived suprathreshold contrast. It has been shown that for grating stimuli contrast detection thresholds depend on spatial frequency, grating area and the number of orientation components. However, suprathreshold contrast perception exhibits contrast constancy, i.e. suprathreshold contrast matches are independent of ...

A hybrid optical-digital signal processing system that estimates the trajectory of moving targets in a two-dimensional field at video frame rates was developed and constructed. The hybrid system is particularly well suited to the trajectory estimation of small, barely discernable, moving objects of unknown position and velocity in high-resolution image sequences. The system uses an optical Four...

I review the operational capabilities of the Chandra X-ray Observatory, including some of the spectacular results obtained by the general observer community. A natural theme of this talk is that Chandra is revealing outflows of great quantities of energy that were not previously observable. I highlight the Chandra studies of powerful X-ray jets. This subject is only possible due to the sub-arcs...

Using metacontrast masking we examined the temporal dynamics of surface completion in object vision. By varying the stimulus onset asynchrony between the target object and the flanking mask(s), we obtained estimates of the time required for the entire surface contrast to fill out within the area delimited by the contours/edges of the target. The estimated speed of the filling-out process was 36...

Several recent studies have related crowding with the feature integration stage in visual processing. In order to understand the mechanisms involved in this stage, it is important to use stimuli that have several features to integrate, and these features should be clearly defined and measurable. In this study, Gabor patches were used as target and distractor stimuli. The stimuli differed in thr...

With luminance gratings, psychophysical thresholds for detecting a small increase in the contrast of a weak 'pedestal' grating are 2-3 times lower than for detection of a grating when the pedestal is absent. This is the 'dipper effect'--a reliable improvement whose interpretation remains controversial. Analogies between luminance and depth (disparity) processing have attracted interest in the e...