Perceptual Grouping of Dots in Noise

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 160-160
Author(s):  
S P Tripathy ◽  
A J Mussap ◽  
H B Barlow
Keyword(s):  
Visual System ◽  
Perceptual Grouping ◽  
Higher Order ◽  
Line Detection ◽  
Order Processing ◽  
Correct Performance ◽  
Single Mechanism ◽  
Series Of Experiments

Observers were asked to report the orientation of alignment (horizontal vs vertical) of a group of target dots embedded in randomly placed noise dots. For this perceptual grouping task, sensitivity (the number of noise dots giving 75% correct performance) was measured as a function of the number of target dots. We report surprising tolerance to positional jitter of target dots, with far less tolerance exhibited to alignment jitter than separation jitter. In this respect, perceptual grouping in our task resembles line detection. In a further series of experiments the target was produced by positional shifts of an appropriate number of noise dots, rather than by addition of target dots to the noise dots (this procedure minimised density cues). The improvement in sensitivity with increasing number of target dots was found to be linear (when plotted on log — log axes) with a slope of 0.5, as opposed to bilinear [cf B Moulden, 1994, in Higher-Order Processing in the Visual System Eds G R Bock, J A Goode (Chichester: John Wiley) pp 170 – 192]. This linearity suggests that, over the range of target dot numbers tested, a single mechanism may be sufficient to explain performance.

Cyclopean Vision, Size Estimation, and Presence in Orthostereoscopic Images

2001 ◽  
Vol 10 (3) ◽  
pp. 312-330 ◽  
Author(s):  
Bernard Harper ◽  
Richard Latto
Keyword(s):  
Visual System ◽  
Three Dimensional ◽  
Point Of View ◽  
Psychophysical Experiment ◽  
Size Estimation ◽  
Human Form ◽  
Image Capture ◽  
Series Of Experiments ◽  
Abstract Shapes ◽  
And Control

Stereo scene capture and generation is an important facet of presence research in that stereoscopic images have been linked to naturalness as a component of reported presence. Three-dimensional images can be captured and presented in many ways, but it is rare that the most simple and “natural” method is used: full orthostereoscopic image capture and projection. This technique mimics as closely as possible the geometry of the human visual system and uses convergent axis stereography with the cameras separated by the human interocular distance. It simulates human viewing angles, magnification, and convergences so that the point of zero disparity in the captured scene is reproduced without disparity in the display. In a series of experiments, we have used this technique to investigate body image distortion in photographic images. Three psychophysical experiments compared size, weight, or shape estimations (perceived waist-hip ratio) in 2-D and 3-D images for the human form and real or virtual abstract shapes. In all cases, there was a relative slimming effect of binocular disparity. A well-known photographic distortion is the perspective flattening effect of telephoto lenses. A fourth psychophysical experiment using photographic portraits taken at different distances found a fattening effect with telephoto lenses and a slimming effect with wide-angle lenses. We conclude that, where possible, photographic inputs to the visual system should allow it to generate the cyclopean point of view by which we normally see the world. This is best achieved by viewing images made with full orthostereoscopic capture and display geometry. The technique can result in more-accurate estimations of object shape or size and control of ocular suppression. These are assets that have particular utility in the generation of realistic virtual environments.

The novel guanylyl cyclase MsGC-I is strongly expressed in higher-order neuropils in the brain of Manduca sexta

2001 ◽  
Vol 204 (2) ◽  
pp. 305-314 ◽  
Author(s):  
A. Nighorn ◽  
P.J. Simpson ◽  
D.B. Morton
Keyword(s):  
Nervous System ◽  
Manduca Sexta ◽  
Guanylyl Cyclase ◽  
Higher Order ◽  
Adult Brain ◽  
Central Complex ◽  
Amino Acid Residues ◽  
Order Processing ◽  
Guanylyl Cyclases ◽  
The Brain

Guanylyl cyclases are usually characterized as being either soluble (sGCs) or receptor (rGCs). We have recently cloned a novel guanylyl cyclase, MsGC-I, from the developing nervous system of the hawkmoth Manduca sexta that cannot be classified as either an sGC or an rGC. MsGC-I shows highest sequence identity with receptor guanylyl cyclases throughout its catalytic and dimerization domains, but does not contain the ligand-binding, transmembrane or kinase-like domains characteristic of receptor guanylyl cyclases. In addition, MsGC-I contains a C-terminal extension of 149 amino acid residues. In this paper, we report the expression of MsGC-I in the adult. Northern blots show that it is expressed preferentially in the nervous system, with high levels in the pharate adult brain and antennae. In the antennae, immunohistochemical analyses show that it is expressed in the cell bodies and dendrites, but not axons, of olfactory receptor neurons. In the brain, it is expressed in a variety of sensory neuropils including the antennal and optic lobes. It is also expressed in structures involved in higher-order processing including the mushroom bodies and central complex. This complicated expression pattern suggests that this novel guanylyl cyclase plays an important role in mediating cyclic GMP levels in the nervous system of Manduca sexta.

Recalibration of Visual Stability Mechanism Occurs in a Higher-Order Visual System

2006 ◽  
Vol 13 (2) ◽  
pp. 111-118
Author(s):  
Kunimitsu Takahara ◽  
Katsunori Okajima ◽  
Masanori Takase
Keyword(s):  
Visual System ◽  
Higher Order ◽  
Visual Stability

The Ternus Effect

2017 ◽  
Author(s):  
Elisabeth Hein
Keyword(s):  
Twentieth Century ◽  
Eye Movements ◽  
Visual System ◽  
Apparent Motion ◽  
Perceptual Grouping ◽  
The Other ◽  
The World ◽  
Motion Display ◽  
In The Beginning ◽  
Insight Into

The Ternus effect refers to an ambiguous apparent motion display in which two or three elements presented in succession and shifted horizontally by one position can be perceived as either a group of elements moving together or as one element jumping across the other(s). This chapter introduces the phenomenon and describes observations made by Pikler and Ternus in the beginning of the twentieth century. Next, reasons for continued interest in the Ternus effect are discussed and an overview of factors that influence it offered, including low-level image-based factors, for example luminance, as well as higher-level scene-based factors, for example perceptual grouping. The chapter ends with a discussion of theories regarding the mechanisms underlying the Ternus effect, providing insight into how the visual system is able to perceive coherent objects in the world despite discontinuities in the input (e.g., as a consequence of eye movements or object occlusion).

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