Investigation of the intersection of constraints model of motion perception

The direction and speed of motion of a one-dimensional (1-D) stimulus, such as a grating, presented within a circular aperture is ambiguous. This ambiguity, referred to as the Aperture Problem (Fennema & Thompson, 1979) results from (i) the inability to detect motion parallel to grating orientation, and (ii) the occlusion of border information, such as the ‘ends’ of the grating, by the surface forming the aperture, Adelson and Movshon's (1982) intcrsection-of-constraints (IOC) model of motion perception describes a two-stage method of disambiguating the motion of 1-D moving stimuli (e.g., gratings) to produce unambiguous motion of two-dimensional (2-D) objects (e.g., plaid patterns) made up of several 1-D components. Specifically, in the IOC model ambiguous 1-D motions extracted by Stage 1 component-selective mechanisms are integrated by Stage 2 pattern-selective mechanisms to produce unambiguous 2-D motion signals. ‘Integration’ in the context of the IOC model involves determining the single motion vector (i.e., combination of direction and speed) which is consistent with the I-D components of a 2-D object. Since the IOC model assumes that 2-D objects undergo pure translation (i.e., without distortion, rotation, etc.), the motion vector consistent with all 1-D components describes the motion of the 2-D object itself. Adelson and Movshon (1982) propose that neural implementation of the computation underlying the IOC model is reflected in the perception of coherent 2-D plaid motion reported when two separately-moving ‘component’ gratings are superimposed. Using these plaid patterns the present thesis assesses the IOC model in terms of its ability to account for the perception of 2-D motion in a variety of circumstances. In the first series of experiments it is argued that the unambiguous motion perceived for a single grating presented within a rectangular aperture (i.e., the Barberpole illusion; Wallach, 1976) reflects application of the IOC computation to the moving 1-D grating and the stationary boundary of the aperture. While contrary to the assumption which underlies the IOC model (viz., that integration occurs between moving 1-D stimuli), evidence consistent with the involvement of the IOC computation in mediating the Barberpole illusion (in which there is only one moving stimulus) is obtained by measuring plaid coherence as a function of aperture shape. It is found that rectangular apertures which bias perceived component motions in directions consistent with plaid direction facilitate plaid coherence, while rectangular apertures which bias perceived component motions in directions inconsistent with plaid direction disrupt plaid coherence. In the second series of experiments, perceived directions of motion of type I symmetrical, type I asymmetrical, and type II plaids are measured with the aim of investigating the deviations in plaid directions reported by Ferrera and Wilson (1990) and Yo and Wilson (1992). Perceived directions of both asymmetrical and type II plaids are shown to deviate away from lOC-predicted directions and towards mean component direction. Furthermore, the magnitude of these deviations is being proportional to the difference between lOC-predicted plaid direction and mean component direction. On the basis of these directional deviations, modification to the IOC model is proposed. In the modified IOC model it is argued that plaid perception involves (i) the activity of Stage 2 pattern-selective mechanisms (and the Stage 1 component-selective mechanisms which input into these pattern-selective mechanisms) involved in implementing the IOC computation, and (ii) component-selective mechanisms which influence plaid perception directly, and ‘extraneously’ to the IOC computation. In the third series of experiments the validity of this modified IOC model, as well as the validity of alternative one-stage models of plaid perception are assessed in relation to perceived directions of plaid-induced MAEs as a function of both plaid direction and mean component direction. It is found that plaid-induced MAEs are shifted away from directions opposite to lOC-predicted plaid direction towards the direction opposite to mean component direction. This pattern of results is taken to be consistent with the modified IOC model which predicts the activity, and adaptation both of mechanisms signalling plaid direction (via implementation of the IOC computation), and ‘extraneous-type’ component-selective mechanisms signalling component directions. Alternative one-stage models which predict the adaptation of only mechanisms signalling plaid direction (the feature-tracking model), or the adaptation only of mechanisms signalling component directions (the distribution-of-activity model), cannot account for the directions of plaid-induced MAEs reported. The ability of the modified IOC model to account for the perceived directions of (i) gratings in rectangular apertures, (ii) various types of plaid in circular apertures, and (iii) directions of plaid-induced MAEs, is interpreted as supporting the proposition that human motion perception is based on a parallel and distributed process involving Stage 2 pattern-selective mechanisms (and the Stage 1 component-selective mechanisms which input into these mechanisms) taken to implement the IOC computation, and component-selective mechanisms taken to provide an 'extraneous' direct contribution to motion perception.

The roles of object-image relative motion and static depth information in the perception of heading

Investigates visual information that enables human to effectively guide their movement through the environment. This problem is fundamental to the study of human behaviour, since survival is contingent upon the acquisition of resources that lie in different locations throughout the environment.

Internal representation of movement in children with developmental coordination disorder : a mental rotation task

Recent studies show that children with developmental coordination disorder (DCD) have difficulties in generating an accurate visuospatial representation of an intended action, which are shown by deficits in motor imagery. This study sought to test this hypothesis further using a mental rotation paradigm. It was predicted that children with DCD would not conform to the typical pattern of responding when required to imagine movement of their limbs. Participants included 16 children with DCD and 18 control children; mean age for the DCD group was 10 years 4 months, and for controls 10 years. The task required children to judge the handedness of single-hand images that were presented at angles between 0° and 180° at 45° intervals in either direction. Results were broadly consistent with the hypothesis above. Responses of the control children conformed to the typical pattern of mental rotation: a moderate trade-off between response time and angle of rotation. The response pattern for the DCD group was less typical, with a small trade-off function. Response accuracy did not differ between groups. It was suggested that children with DCD, unlike controls, do not automatically enlist motor imagery when performing mental rotation, but rely on an alternative object-based strategy that preserves speed and accuracy. This occurs because these children manifest a reduced ability to make imagined transformations from an egocentric or first-person perspective.

Maternity

Fruiting bodies represents human engagement with and consciousness of a corresponding presence in our landscape. ʻFruiting Bodiesʼ is an instance of the application of this practice employed to ask the viewer to consider how strange is the phenomenon of the fruiting tree. Is it promiscuous to offer your seed openly to the elements, to any who will take it. Is this forbidden? Is it profligate to hide your progeny inside gifts so tempting in their appeal to that most primitive desire, hunger? Is this wholly mere biological expedience evolved to ensure the widest migration of your offspring? Or does it derive from some boundless cosmic generosity? These images invite you to come close to the tree, where within its arms you will find shelter from the sun at its zenith and from the autumnal rains. Fruit is the focus of Jamesʼs lens as it circles deep into the embrace of limbs and leaves.

Luxe

Fruiting bodies represents human engagement with and consciousness of a corresponding presence in our landscape. ʻFruiting Bodiesʼ is an instance of the application of this practice employed to ask the viewer to consider how strange is the phenomenon of the fruiting tree. Is it promiscuous to offer your seed openly to the elements, to any who will take it. Is this forbidden? Is it profligate to hide your progeny inside gifts so tempting in their appeal to that most primitive desire, hunger? Is this wholly mere biological expedience evolved to ensure the widest migration of your offspring? Or does it derive from some boundless cosmic generosity? These images invite you to come close to the tree, where within its arms you will find shelter from the sun at its zenith and from the autumnal rains. Fruit is the focus of Jamesʼs lens as it circles deep into the embrace of limbs and leaves.

Lust

Fruiting bodies represents human engagement with and consciousness of a corresponding presence in our landscape. ʻFruiting Bodiesʼ is an instance of the application of this practice employed to ask the viewer to consider how strange is the phenomenon of the fruiting tree. Is it promiscuous to offer your seed openly to the elements, to any who will take it. Is this forbidden? Is it profligate to hide your progeny inside gifts so tempting in their appeal to that most primitive desire, hunger? Is this wholly mere biological expedience evolved to ensure the widest migration of your offspring? Or does it derive from some boundless cosmic generosity? These images invite you to come close to the tree, where within its arms you will find shelter from the sun at its zenith and from the autumnal rains. Fruit is the focus of Jamesʼs lens as it circles deep into the embrace of limbs and leaves.

Glance

Fruiting bodies represents human engagement with and consciousness of a corresponding presence in our landscape. ʻFruiting Bodiesʼ is an instance of the application of this practice employed to ask the viewer to consider how strange is the phenomenon of the fruiting tree. Is it promiscuous to offer your seed openly to the elements, to any who will take it. Is this forbidden? Is it profligate to hide your progeny inside gifts so tempting in their appeal to that most primitive desire, hunger? Is this wholly mere biological expedience evolved to ensure the widest migration of your offspring? Or does it derive from some boundless cosmic generosity? These images invite you to come close to the tree, where within its arms you will find shelter from the sun at its zenith and from the autumnal rains. Fruit is the focus of Jamesʼs lens as it circles deep into the embrace of limbs and leaves.

Gyration

European Renaissance and Romantic landscape appeared in vistas. The conditions of the industrial revolution and, according to Patrick Maynard and Jonathon Crary, the film camera especially, led to a Modernist re-vision vividly recorded in Xavier Herbert’s contrary Modernist vision, prompted by seeing the Australian bush, its ‘... stunted trees, the mulga and the wilga and the gimlet gum, doing a kind of dance, spinning past, seeming to swing away from the train to the horizon and race ahead, to come back...the same set of trees in endless gyration’.

The roles of static depth information and object-image relative motion in perception of heading

In a series of 6 experiments, two hypotheses were tested: that nominal heading perception is determined by the relative motion of images of objects positioned at different depths (R. F. Wang & J. E. Cutting 1999) and that static depth information contributes to this determination. By manipulating static depth information while holding retinal-image motion constant during  simulated self-movement, the authors found that static depth information played a role in determining perceived heading. Some support was also found for the involvement of R. F. Wang and J. E. Cutting’s (1999) categories of object-image relative motion in determining perceived heading. However, results suggested an unexpected functional dominance of information about heading relative to apparently near objects.

Incorporating human perception with the motion washout filter using fuzzy logic control

Abstract—Nowadays, classical washout filters are extensively used in commercial motion simulators. Even though there are several advantages for classical washout filters, such as short processing time, simplicity and ease of adjustment, they have several shortcomings. The main disadvantage is the fixed scheme and parameters of the classical washout filter cause inflexibility of the structure and thus the resulting simulator fails to suit all circumstances. Moreover, it is a conservative approach and the platform cannot be fully exploited. The aim of this research is to present a fuzzy logic approach and take the human perception error into account in the classical motion cueing algorithm, in order to improve both the physical limits of restitution and realistic human sensations. The fuzzy compensator signal is applied to adjust the filtered signals on the longitudinal and rotational channels online, as well as the tilt coordination to minimize the vestibular sensation error below the human perception threshold. The results indicate that the proposed fuzzy logic controllers significantly minimize the drawbacks of having fixed parameters and conservativeness in the classical washout filter. In addition, the performance of motion cueing algorithm and human perception for most occasions is improved.

Hyperstereopsis in helmet-mounted NVDs : slope perception

Modern helmet-mounted night vision devices, such as the Thales TopOwl helmet, project imagery from intensifiers mounted on the sides of the helmet onto the helmet faceplate. This produces a situation of hyperstereopsis in which binocular disparities are magnified. This has the potential to distort the perception of slope in depth (an important cue to landing), because the slope cue provided by binocular disparity conflicts with veridical cues to slope, such as texture gradients and motion parallax. In the experiments, eight observers viewed sparse and dense textured surfaces tilted in depth under three viewing conditions: normal stereo hyper-stereo (4 times magnification), and hypostereo (1 / 4 magnification). The surfaces were either stationary, or rotated slowly around a central vertical axis. Stimuli were projected at 6 metres to minimise conflict between accommodation and convergence, and stereo viewing was provided by a Z-screen and passive polarised glasses. Observers matched perceived visual slope using a small tilt table set by hand. We found that slope estimates were distorted by hyperstereopsis, but to a much lesser degree than predicted by disparity magnification. The distortion was almost completely eliminated when motion parallax was present.

Postural neck pain : an investigation of habitual sitting posture, perception of 'good' posture and cervicothoracic kinaesthesia

Impairments of cervico-cephalic kinaesthesia and habitual forward head posture have been considered important in the aetiology of postural neck pain, yet these factors have not been specifically examined in a homogeneous clinical population. The objective of this study was to compare the habitual sitting posture (HSP), perception of good posture and postural repositioning error (PRE) of the cervico-thoracic (CT) spine in individuals with postural neck pain, with a matched group of asymptomatic subjects. Twenty-one subjects with postural neck pain and 22 asymptomatic control subjects were recruited into the study. An optical motion analysis system was used to measure the HSP and perceived ‘good’ sitting posture. PRE was measured over six trials where the subject attempted to replicate their self-selected ‘good’ posture. There was no difference between the groups in the HSP but significant differences were identified in the perception of ‘good’ posture. Posture repositioning error was higher for the head posture variables than for CT and shoulder girdle variables in both groups. However, there was no significant difference in posture repositioning error between groups for any of the posture measures. The findings suggest that individuals with postural neck pain may have a different perception of ‘good’ posture, but no significant difference in HSP or kinaesthetic sensibility compared with matched asymptomatic subjects.