Visual perception

How does spatial organization of objects affect the perceptual processing of a scene? Surprisingly, little research has explored this topic. A few studies have reported that, when simple, homogenous stimuli (e.g., dots), are presented in a regular formation, they are judged to be more numerous than when presented in a random configuration (Ginsburg, 1976; 1978). However, these results may not apply to real-world objects. In the current study, fewer objects were believed to be on organized desks than their disorganized equivalents. Objects that are organized may be more likely to become integrated, due to classic Gestalt principles. Consequently, visual search may be more difficult. Such object integration may diminish saliency, making objects less apparent and more difficult to find. This could explain why, in the present study, objects on disorganized desks were found faster.

The dissertation is about the significance for, and impact upon public administration of the correspondence theory of truth or veridicality, and its underlying epistemological assumptions. The underlying thesis is that, unduly influenced by the success of the natural sciences, and naive in accepting their claims to objectivity, many disciplines have sought to emulate them. There are two principle objections. Firstly, all other considerations aside, the supposedly objectivistic methodologies apparently applied to the explanation and prediction of the behavior of interactions of physical objects, may simply be inappropriate to certain other areas of inquiry; and more specifically objectivist methodologies are indeed inappropriate to understanding of human subjects, and their behavior, relations and interactions, and thus to public administration. The second objection is that it is of course logically impossible for any supposedly empirical discipline, as the natural sciences claim to be, to justify the belief in a supposedly objective realm of things-in-themselves existing outside, beyond, or independently of the changing, interrupted and different 'appearances' or experiences, to which an empirical science is qua empirical, necessarily restricted. Correspondence of any empirical observations or appearances (and the consequent or presupposed theoretical explanations) to an objective realm, upon which the claim to objectivity is based, is unverifiable. In light of the above it becomes evident that far from being objective, the natural sciences themselves, and the empirical observations upon which they are supposedly grounded, are subject to conceptual mediation and subjective interpretation; subjective and inter-subjective coherence replacing objective correspondence as the criterion of veridicality. Consequently it becomes clear that the presuppositions and prejudices of the observers enter, in the forms of concepts and preconceptions, into the very observations, and even more so into the theoretical constructions, or theories, of the natural, and indeed human and social sciences, and their claims to be authoritative and true. Subsequent discussion is then focused on both the coherence of individuals' experiences and understanding, and their inter-subjective coherence - which both rises from and constitutes, a "community". The role of language facilitates such coherence.

Prior research has explored the counterchange model of motion detection in terms of counterchanging information that originates in the stimulus foreground (or objects). These experiments explore counterchange apparent motion with regard to a new apparent motion stimulus where the necessary counterchanging information required for apparent motion is provided by altering the luminance of the background. It was found that apparent motion produced by background-counterchange requires longer frame durations and lower levels of average stimulus contrast compared to foreground-counterchange. Furthermore, inter-object distance does not influence apparent motion produced by background-counterchange to the degree it influences apparent motion produced by foreground-counterchange.

The perception of visual motion is an integral aspect of many organisms' engagement with the world. In this dissertation, a theory for the perception of visual object-motion is developed. Object-motion perception is distinguished from objectless-motion perception both experimentally and theoretically. A continuoustime dynamical neural model is developed in order to generalize the ndings and provide a theoretical framework for continued re nement of a theory for object-motion
perception. Theoretical implications as well as testable predictions of the model are discussed.

The effects of the onset, offset, and sustained presence of inducing lines on the perceived position of test lines were independently investigated in a vernier alignment task. For spatial separations larger than 2.3 min, repulsion effects were always observed. For the smallest spatial separation, 2.3 min, the effect of the inducing lines was attraction for 0 and 195 SOAs. Minimal attraction was observed for a 3000 SOA. However, when the offset effect was isolated using the 3000 SOA and a 0 ISI, a large repulsion effect was observed for the 2.3 min spatial separation, as well as for the larger spatial separations. These results indicate that the temporal separation between visual elements is as important in determining perceived position as their spatial separation, which has been demonstrated in earlier studies (Badcock & Westheimer, 1985). A differential gradient model is proposed which accounts for these findings in terms of excitatory and inhibitory interactions within an ensemble of position-sensitive units.

Anstis, et al. (1985) have reported that under certain conditions the visual system adapts and the perception of apparent motion breaks down. The present research indicates that breakdown is actually a result of same-place mechanisms successfully competing with motion-detecting mechanisms. Thus, the perception of stationarity (with flicker) can occur at the start of a trial and spontaneously switch to the perception of motion, or vice versa. The response of same-place mechanisms depends on the zero-hertz energy at each location of an apparent motion stimulus, whereas the response of motion mechanisms depends on the time-varying energy. Average luminance, luminance contrast, the temporal symmetry of the apparent motion display, and relative phase are manipulated to investigate competition between same-place and motion-detecting mechanisms.

This research investigated whether choice reaction time (RT) measures and the P300 component of the event-related brain potential (ERP) could be employed to index the attentional resources associated with performing two near-simultaneous tasks. Specifically, this study investigated the effects of auditory tones on the ERPs and RTs associated with a visual stimulus when the stimuli in both modalities were presented in close temporal proximity. The hypothesis that the ERPs and RTs elicited by the deviant visual stimulus would index the processing demands associated with the auditory modality was confirmed. In general, greater P300 amplitude associated with one task indicates diminished P300 and poorer performance on a second task. The results indicate that P300 may be a sensitive indicator of shared processing resources when two tasks are performed near simultaneously.

This thesis studies the 2-D-based visual invariant that exists during relative motion between a camera and a 3-D object. We show that during fixation there is a measurable nonlinear function of optical flow that produces the same value for all points of a stationary environment regardless of the 3-D shape of the environment. During fixated camera motion relative to a rigid object, e.g., a stationary environment, the projection of the fixated point remains (by definition) at the same location in the image, and all other points located on the 3-D rigid object can only rotate relative to that 3-D fixation point. This rotation rate of the points is invariant for all points that lie on the particular environment, and it is measurable from a sequence of images. This new invariant is obtained from a set of monocular images and is expressed explicitly as a closed form solution.

A barrier to the use of digital imaging is the vast storage requirements involved. One solution is compression. Since imagery is ultimately subject to human visual perception, it is worthwhile to design and implement an algorithm which performs compression as a function of perception. The underlying premise of the thesis is that if the algorithm closely matches visual perception thresholds, then its coded images contain only the components necessary to recreate the perception of the visual stimulus. Psychophysical test results are used to map the thresholds of visual perception, and develop an algorithm that codes only the image content exceeding those thresholds. The image coding algorithm is simulated in software to demonstrate compression of a single frame image. The simulation results are provided. The algorithm is also adapted to real-time video compression for implementation in hardware.

This research was concerned with the perception of inter-element
distance and angle relations for pairs of dots arranged vertically,
horizontally, oblique-left, and oblique-right. For each trial, a pair
of dots was presented in different global locations, for five
consecutive frames. The subject's task was to detect a change in the
relative location of the dots, which could occur during one of the
five frames. Each subject participated in three different conditions.
One condition emphasized the detection of changes in distance between
the elements; the second emphasized the detection of changes in the
angle formed by the elements. The third condition did not focus
attention on either distance or angle changes. Results indicated that
focussing attention on either distance or angle changes affected
sensitivity to distance changes for rectilinear, but not for oblique
arrangements. These results suggested that the vertical and horizontal
components of Inter-element distance are perceptually fundamental, and
that the Euclidean distance between two elements and the angle formed by
the elements are internally computed from the perceptually fundamental
distance components.