Spelling suggestions: "subject:"apatial vision"" "subject:"cpatial vision""
1 |
Contrast Sensitivity to One- and Two-Dimensional Luminance PatternsPersaud, Steven S. 14 May 2004 (has links)
Contrast sensitivities to one- and two-dimensional luminance patterns were compared in a two-alternative forced choice (2AFC) experiment. Space-averaged luminance was also manipulated. Statistical analyses revealed a main effect of stimulus dimension (p < .05) and no effect of space-averaged luminance. The main effect of stimulus dimension was explained in terms of an on-center, off-center receptive field model combined with watershed spatial vision behavior at spatial frequencies below 1 cycle-per-degree (cpd). The non-significant result for space-averaged luminance was explained by the limited range of manipulation of the variable. Two-dimensional luminance patterns were suggested as ideal patterns for reconciling grating-based spatial vision research with spatial vision behavior in an ecological context. Future research directions are suggested. / Master of Science
|
2 |
Evidence for chromatic edge detectors in human vision using classification imagesMcIlhagga, William H., Mullen, K.T. 07 September 2018 (has links)
Yes / Edge detection plays an important role in human vision,
and although it is clear that there are luminance edge
detectors, it is not known whether there are chromatic
edge detectors as well.We showed observers a horizontal
edge blurred by a Gaussian filter (with widths of r ¼
0.1125, 0.225, or 0.458) embedded in blurred Brown
noise. Observers had to choose which of two stimuli
contained the edge. Brown noise was used in preference
to white noise to reveal localized edge detectors. Edges
and noise were defined by either luminance or chromatic
contrast (isoluminant L/M and S-cone opponent).
Classification image analysis was applied to observer
responses. In this analysis, the random components of the
stimulus are correlated with observer responses to reveal
a template that shows how observers weighted different
parts of the stimulus to arrive at their decision.We found
classification images for both luminance and isoluminant
chromatic stimuli that had shapes very similar to
derivatives of Gaussian filters. The widths of these
classification images tracked the widths of the edges, but
the chromatic edge classification images were wider than
the luminance ones. These results are consistent with
edge detection filters sensitive to luminance contrast and
isoluminant chromatic contrast. / Royal Society Travel Grant IE130877 and in part by Canadian Institutes of Health Research (CIHR) grant MOP-10819
|
3 |
Retina-V1 model of detectability across the visual fieldBradley, Chris Kent 22 September 2014 (has links)
A practical model is proposed for predicting the detectability of targets at arbitrary locations in the visual field, in arbitrary gray-scale backgrounds, and under photopic viewing conditions. The major factors incorporated into the model include: (i) the optical point spread function of the eye, (ii) local luminance gain control (Weber's law), (iii) the sampling array of retinal ganglion cells, (iv) orientation and spatial-frequency dependent contrast masking, (iv) broadband contrast masking, (vi) and efficient response pooling. The model is tested against previously reported threshold measurements on uniform backgrounds (the ModelFest data set and data from Foley et al. 2007), and against new measurements reported here for several ModelFest targets presented on uniform, 1/f noise, and natural backgrounds, at retinal eccentricities ranging from 0 to 10 deg. Although the model has few free parameters, it is able to account quite well for all the threshold measurements. / text
|
4 |
Visual perception of gradients. A psychophysical study of the mechanisms of detection and discrimination of achromatic and chromatic gradients.Garcia-Suarez, Luis January 2009 (has links)
No description available.
|
5 |
Severe loss of positional information when detecting deviations in multiple trajectoriesTripathy, Srimant P., Barrett, Brendan T. January 2004 (has links)
No / Human observers can simultaneously track up to five targets in motion (Z. W. Pylyshyn & R. W. Storm, 1988). We examined the precision for detecting deviations in linear trajectories by measuring deviation thresholds as a function of the number of trajectories (T ). When all trajectories in the stimulus undergo the same deviation, thresholds are uninfluenced by T for T <= 10. When only one of the trajectories undergoes a deviation, thresholds rise steeply as T is increased [e.g., 3.3º (T = 1), 12.3º (T = 2), 32.9º (T = 4) for one observer]; observers are unable to simultaneously process more than one trajectory in our threshold-measuring paradigm. When the deviating trajectory is cued (e.g., using a different color), varying T has little influence on deviation threshold. The use of a different color for each trajectory does not facilitate deviation detection. Our current data suggest that for deviations that have low discriminability (i.e., close to threshold) the number of trajectories that can be monitored effectively is close to one. In contrast, when the stimuli containing highly discriminable (i.e., substantially suprathreshold) deviations are used, as many as three or four trajectories can be simultaneously monitored (S. P. Tripathy, 2003). Our results highlight a severe loss of positional information when attempting to track multiple objects, particularly in a threshold paradigm.
|
6 |
Large crowding zones in peripheral vision for briefly presented stimuliTripathy, Srimant P., Cavanagh, P., Bedell, H.E. 12 1900 (has links)
Yes / When a target is flanked by distractors, it becomes more
difficult to identify. In the periphery, this crowding effect
extends over a wide range of target-flanker separations,
called the spatial extent of interaction (EoI). A recent
study showed that the EoI dramatically increases in size
for short presentation durations (Chung & Mansfield,
2009). Here we investigate this duration-EoI relation in
greater detail and show that (a) it holds even when
visibility of the unflanked target is equated for different
durations, (b) the function saturates for durations
shorter than 30 to 80 ms, and (c) the largest EoIs
represent a critical spacing greater than 50% of
eccentricity. We also investigated the effect of same or
different polarity for targets and flankers across different
presentation durations. We found that EoIs for target
and flankers having opposite polarity (one white, the
other black) show the same temporal pattern as for
same polarity stimuli, but are smaller at all durations by
29% to 44%. The observed saturation of the EoI for shortduration
stimuli suggests that crowding follows the locus
of temporal integration. Overall, the results constrain
theories that map crowding zones to fixed spatial
extents or to lateral connections of fixed length in the
cortex. / This study was supported by the ERC POSITION 324070 (PC) and a visiting professorship to Anglia Ruskin University from the Leverhulme Trust (HEB).
|
7 |
Investigating the role of spatial frequency bands in drawingFreeman, Tyler E. January 1900 (has links)
Master of Science / Department of Psychology / Lester C. Loschky / To investigate the role of various bands of spatial frequencies for drawing, untrained artists drew four portraits from four different bands of spatial frequencies (e.g. unfiltered, 4-8, 8-16, & 16-32 cycles per face width (c/fw)). Raters then judged the accuracy of the drawings in comparison to both the source image from which the drawings were produced and an unfiltered version of the same face. The results show that low spatial frequencies (LSFs) and high spatial frequencies (HSFs) were useful for drawing, relative to middle spatial frequencies (MSFs). Additionally, the unfiltered condition that contained all spatial frequencies produced the most accurate drawings. This suggests that when artists are allowed access to both LSFs and HSFs they are able to utilize the global structure information carried in LSFs as well as the edge and detail information carried in HSFs to create more accurate drawings. The author posits that the MSFs that are useful for face recognition become redundant for drawing and that novice artists discount these MSFs in the control condition in order to increase the saliency and usefulness of the LSFs and HSFs. The results have implications for art education, drawing technology and the development of low-level drawing theory.
|
8 |
Visual perception of gradients : a psychophysical study of the mechanisms of detection and discrimination of achromatic and chromatic gradientsGarcia-Suarez, Luis January 2009 (has links)
No description available.
|
9 |
Distinct lower visual field preference for object shapeSchmidtmann, G., Logan, Andrew J., Kennedy, Graeme J., Gordon, G.E., Loffler, G. 2015 April 1929 (has links)
Yes / Humans manipulate objects chiefly within their lower visual field, a consequence of upright posture and the anatomical position of hands and arms.This study tested the hypothesis of enhanced sensitivity to a range of stimuli within the lower visual field. Following current models of hierarchical processing within the ventral steam, discrimination sensitivity was measured for orientation, curvature, shape (radial frequency patterns), and faces at various para-central locations (horizontal, vertical, and main diagonal meridians) and eccentricities (5° and 10°). Peripheral sensitivity was isotropic for orientation and curvature. By contrast, observers were significantly better at discriminating shapes throughout the lower visual field compared to elsewhere. For faces, however, peak sensitivity was found in the left visual field, corresponding to the right hemispheric localization of human face processing. Presenting head outlines without any internal features (e.g., eyes, mouth) recovered the lower visual field advantage found for simple shapes. A lower visual field preference for the shape of an object, which is absent for more localized information (orientation and curvature) but also for more complex objects (faces), is inconsistent with a strictly feed-forward model and poses a challenge for multistage models of object perception. The distinct lower visual field preference for contour shapes is, however, consistent with an asymmetry at intermediate stages of visual processing, which may play a key role in representing object characteristics that are particularly relevant to visually guided actions.
|
10 |
Investigating the Relationship between Binocular Disparity, Viewer Discomfort, and Depth Task Performance on Stereoscopic 3D DisplaysMcIntire, John Paul 04 June 2014 (has links)
No description available.
|
Page generated in 0.076 seconds