Motion Of Gratings Research Articles

Barber-pole illusions and plaids: the influence of aperture shape on motion perception.

The barber-pole illusion and its influence on plaid perception were investigated in two experiments to test the following expectations: (i) apertures which bias the perception of grating motion in directions consistent with plaid direction will facilitate plaid perception, and (ii) apertures which bias the perception of grating motion in directions inconsistent with plaid direction will disrupt plaid perception. In experiment 1 the barber-pole illusion was measured as a function of grating orientation (20 degrees, 45 degrees, and 70 degrees, clockwise and counterclockwise from horizontal), and aperture shape (vertical, horizontal; at each of three elongations). Barber-pole illusions reported with 45 degrees gratings increased with increased aperture elongation. However, this was not found with 20 degrees and 70 degrees gratings; these were almost always reported as moving in a direction parallel to the side of the aperture with which the gratings formed angles approaching 90 degrees. In experiment 2 this dependence of barber-pole illusions on the relative orientation between gratings and apertures was also evident with 45 degrees gratings in oblique apertures; only oblique directions of grating motion were reported. The influence of the same apertures on the separate contrast thresholds required for initial plaid coherence and initial plaid decomposition was measured. In experiments 1 and 2, coherence thresholds were unaffected by apertures, contrary to expectation (i). However, in both experiments expectation (ii) was confirmed; decomposition thresholds decreased in apertures which biased perceived direction of gratings towards vertical (plaid direction), and increased in apertures which biased grating motion away from vertical. Adaptation of plaid mechanisms during measurement of decomposition thresholds was proposed to explain the discrepancy between coherence and decomposition data. Taken together, the results were interpreted as reflecting interactions between mechanisms mediating the barber-pole illusion and mechanisms mediating plaid perception.

Optical Bistability and Multistability in the Linear Photorefractive Oscillator Accompanied by a Frequency Shift Due to Grating Motion

Abstract We investigate the bistable and multistable response of the phase conjugate reflectivity (PCR) for the case of a linear photorefractive (PR) oscillator in presence of the moving grating operation. Numerical evaluation of stable multiple solutions of the PCR shows enhancement, bistable, multistable and self-oscillating behaviours with respect to the control parameters like the frequency-shift (Ω) due to grating motion, reflectivities (M 1 and M 2) of cavity mirrors, the coupling strength (of complex gL and real g 0 L values) and the PR phase shift (φPR). If the different branches are assumed to be stable, multistable but isolated branching behaviour with an increased PCR can be predicted. Results are interpreted physically by considering the competitions between (i) the strengths of two moving transmission gratings that arise from A1–A4 (forward oscillating pump-incident) and A2–A3 (backward oscillating pump-phase conjugate) interferences and (ii) the applied frequency detuning that causes the gra...

Detecting and discriminating the direction of motion of luminance and colour gratings

Human observers were required to discriminate the direction of motion of vertically moving, 1 c/deg luminance and colour gratings. The gratings had different contrasts and moved at temporal frequencies between 0.5 and 32 Hz. Sensitivity [the reciprocal of the contrast at which performance reached 75% correct in a temporal two-alternative forced-choice (2 AFC) discrimination task] was a band-pass function of temporal frequency for luminance gratings, and a low-pass function of temporal frequency for colour gratings. Further, when colour contrast was expressed in terms of the modulation in cone excitation produced by the stimulus, sensitivity to colour gratings was greater than sensitivity to luminance gratings at frequencies below 2 Hz. On the other hand, at temporal frequencies above 4 Hz, sensitivity to colour gratings was comparable with sensitivity to luminance gratings of double the temporal frequency. Detection sensitivity was measured for luminance and colour gratings of 1, 4 and 16 Hz. With either colour or luminance gratings, detection thresholds were very similar to those for direction-of-motion discrimination. This result confirms findings of Mullen and Boulton [(1992) Vision Research, 32, 483–488] and Cavanagh and Anstis [(1991) Vision Research, 31, 2109–2148], but is different from that reported by Lindsey and Teller [(1990) Vision Research, 30,1751–1761] who used a smaller stimulus seen in a parafoveal region and found that motion discrimination thresholds were higher than detection threshold for colour gratings. We repeated our threshold measurements using parafoveal viewing conditions similar to those used by Lindsey and Teller (1990). We found that, although for luminance gratings detection thresholds were very close to direction-discrimination thresholds, for colour gratings, they were lower. The result is in qualitative agreement with Lindsey and Teller (1990). Our results suggest that low-level, or “first-order” motion mechanisms are not as sensitive to chromatic gratings as are colour-detection mechanisms.

Spatial gating effects on judged motion of gratings in apertures.

Wallach has described in qualitative terms the movement of lines behind apertures. We related the data he obtained to the aperture problem, constructed a model of movement perception, and carried out tests of the model. Experiment 1 was a parametric study, and showed the conditions under which a reliable illusion (the barber pole illusion) of diagonal movement of lines along an aperture could be obtained, and when fluctuating judgements or veridical percepts were obtained. On the basis of this study a dipole model was constructed. The model was further developed and tested. In experiment 2 the effects of total area of stimulation were examined: diagonal gratings were viewed behind multiple apertures. In experiment 3 the effects of local signs were examined: diagonal gratings were viewed in an aperture which had edges cut in small steps and stairs, with the risers parallel to the grating, and the treads parallel to the direction of motion of the grating. Experiment 4 was designed to test a prediction about the motion aftereffect of dots near and far from the point of fixation, and the results confirmed the model. It was concluded that the model accounts for the barber pole illusion and, generally, for the movement of gratings in apertures.

Neural circuits mediating visual flight control in flies. II. Separation of two control systems by microsurgical brain lesions

The role of 2 sets of interneurons in the optic lobes of blowflies in visual course control was studied by means of brain lesions. The first set comprises the cells HS and H2, which respond to global horizontal motion. The second set are the FD-cells, which respond selectively to local horizontal motion. All these cells are output neurons of the third optic ganglion of flies and are thought to be coupled via descending neurons to the flight motor system. In 2 series of experiments specific cells of these 2 sets were inactivated by microsurgical brain lesions L1 and L2 respectively. The effects of the lesions on visual course control were tested by measuring the yaw torque responses of the animals in restrained flight before and after the operation. The flies were stimulated in these tests with monocular and binocular motion of periodic gratings moving in either the horizontal or the vertical direction. Lesion L1 in the right side of the brain inactivates the right HS-cells and the left H2- and FD-cells. This leads to a complete block of the response to binocular clockwise horizontal motion and a reduction of the response to monocular motion from front to back on the right side of the animal. Application of L1 also leads to a pronounced response to binocular motion from front to back not observed in normal animals. The response to monocular vertical motion is unaffected. Lesion L2 reduces all responses to monocular and binocular horizontal motion present in normal animals. The behavioral effects of the lesions are highly specific and consistent with predictions based on the well-known anatomical and physiological properties of the neural circuitry investigated. The results demonstrate directly that the HS-, H2-, and FD-cells control motion-induced steering maneuvers in flight.

Photoinduced phenomena in LiNbO3crystals

Abstract The review on the photoinduced phenomena in LiNbO3 crystals is presented. The various types of light induced scattering are described. It is shown that periodic oscillations of scattering fan and photogalvanic current and photodestruction effect are the result of dynamics of space charge field formation. The observed motion of phase grating in crystal during its dark relaxation is explained by the propagation of trap recharging waves. Their specific dispersion law v ∼ K -2 agrees with experiment.

Growth and characterization of large Tl3AsSe3 crystals for collinear AOTF devices

Several high quality Tl 3 AsSe 3 single crystals were grown by the Bridgman-Stockbarger method. Crystals of 25 mm diameter, 10 cm length and b axis orientation (with respect to hexagonal representation) were used to fabricate the devices. Acousto-Optic Tunable Filters (AOTF) were built from these crystals to achieve rapid, agile wavelength tuning of CO 2 laser outputs without resorting to mechanical movement of gratings, prisms or other such types of dispersive devices. Successful demonstration of intra-cavity AOTF tuning was carried out. The device provided intra-cavity tuning over the high gain P and R branch transitions of the (001)–(100) CO 2 band.

Thresholding semilinear phase-conjugate mirror

We have demonstrated thresholding in a semilinear self-pumped phase-conjugate mirror by introducing grating motion within the photorefractive crystal and using the dependence of photorefractive response time on the intensity of the incident beam. The threshold level Ith was found to be a function of the grating velocity. This property has potential applications in optical computing and optical signal processing.

Abolition of visual cortical direction selectivity affects visual behavior in cats.

We reared cats in an environment illuminated stroboscopically at 8 Hz, and studied their ability to detect and discriminate the direction of motion of sinusoidal gratings. Normal cats, like humans, could discriminate the direction of a grating's motion at contrasts that are just barely visible. Strobe-reared cats could detect the grating at contrasts similar to those required by normal cats, but required contrasts that were about 10 times threshold to identify the direction of motion. We subsequently studied the activity of single units in the striate cortex in these cats, and found that directional motion selectivity--normally a prominent feature of striate cortical neurons--was almost absent; other cortical receptive field properties were roughly normal. These results suggest that directionally selective neurons are involved in visual discriminations based on the direction of motion.

Lower thresholds of motion for gratings as a function of eccentricity and contrast

We investigated the lower threshold for motion (LTM) of gratings as a function of position in the visual field, spatial frequency and contrast and we compared motion thresholds for sine wave and square wave luminance profiles. For contrasts below 0.05 the lower threshold for motion was raised; the increase in threshold being dependent upon spatial frequency. At contrast levels above 0.05. LTM was found to be a constant velocity at any given spatial location but increased with eccentricity of view. Raised thresholds for motion at eccentric locations could be compensated by increasing the size of eccentric gratings in proportion to M −2, where M is the cortical magnification factor, a procedure which standardises the cortical representation at differing eccentricities. Thus LTM could be expressed as a constant cortical velocity for grating contrasts above 0.05 at all stimulus locations investigated. We interpret our data as support for a ratio model of velocity coding.

Spatial and velocity tuning of processes underlying induced motion

A nulling procedure was used to quantify the velocity and spatial frequency tuning of induced motion for sinusoidal gratings. For each spatial frequency of test and inducing gratings, there was a range of low velocities which resulted in strong induction, with a gain of close to 1. For low spatial frequencies induction occurred at higher velocities than was the case for high spatial frequencies. Induced motion shows bandpass spatial frequency tuning, with a bandwidth of about two octaves at half-height. Induced motion appears to be mediated by spatial channels with a low pass temporal characteristic. To a first approximation, induced motion appears to be a product of velocity and spatial frequency.

Is the landing response of the housefly (Musca) driven by motion of a flow field?

The landing response of tethered flying housefliesMusca domestica elicited by motion of periodic gratings is analysed. The field of view of the compound eyes of a fly can be subdivided into a region of binocular overlap and a monocular region. In the monocular region the landing response is elicited by motion from front to back and suppressed by motion from back to front. The sensitivity to front to back motion in monocular flies (one eye covered with black paint) has a maximum at an angle 60°–80° laterally from the direction of flight in the equatorial plane. The maximum of the landing response to front to back motion as a function of the contrast frequencyw/λ is observed at around 8 Hz. In the region of binocular overlap of monocular flies the landing response can be elicited by back to front motion around the equatorial plane if a laterally positioned pattern is simulataneously moved from front to back. 40° above the equatorial plane in the binocular region the landing response in binocular flies is elicited by upward motion, 40° below the equatorial plane in the binocular region it is elicited by downward motion. The results are interpreted as an adaptation of the visual system of the fly to the perception of a flow field having its pole in the direction of flight.