Global ETD Search

1	Evidence for chromatic edge detectors in human vision using classification images McIlhagga, 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 Colour vision Edges Spatial vision Classification images
2	Contrast Sensitivity to One- and Two-Dimensional Luminance Patterns Persaud, 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 spatial vision Fourier analysis luminance contrast sensitivity
3	Retina-V1 model of detectability across the visual field Bradley, 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 Spatial vision Detection Masking Peripheral vision Ganglion cells Natural images
4	Severe loss of positional information when detecting deviations in multiple trajectories Tripathy, 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. Multiple Object Tracking Attention Deviation Detection Spatial Vision Motion Perception
5	Large crowding zones in peripheral vision for briefly presented stimuli Tripathy, 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).
6	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. Human vision Spatial vision Colour vision Psychophysics Gradients Detection Discrimination
7	Investigating the role of spatial frequency bands in drawing Freeman, 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. Art Drawing Face Perception Spatial Frequency Spatial Vision Psychology, Cognitive (0633)
8	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. 617.7
9	Distinct lower visual field preference for object shape Schmidtmann, G., Logan, Andrew J., Kennedy, Graeme J., Gordon, G.E., Loffler, G. 29 April 2015 (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 Displays McIntire, John Paul 04 June 2014 (has links) No description available. Psychology Quantitative Psychology Robotics Robots Scientific Imaging Technology Behavioral Sciences Cognitive Psychology Engineering Experimental Psychology Experiments Medical Imaging Ophthalmology Optics stereoscopy binocular vision phoria vergence fusion optometry 3D depth perception spatial vision display design virtual camera teleoperation microstereopsis orthostereopsis virtual environment simulator sickness viewer discomfort

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