Contrast and Contextual Effects: Detection of Subthreshold Lines

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 177-177 ◽  
Author(s):  
C Wehrhahn ◽  
B Dresp
Keyword(s):  
Visual Processing ◽  
Contextual Effects ◽  
Detection Thresholds ◽  
Preliminary Results ◽  
Contrast Polarity ◽  
Early Stages ◽  
Relative Contrast ◽  
Mere Presence ◽  
Opposite Contrast

Contextual effects of collinear lines and features on the processing of line targets, finding expression in detection facilitation, have been described recently in the literature (Dresp and Bonnet, 1995 Vision Research35 1071 – 1078; Kapadia, Ito, Gilbert, and Westheimer, 1995 Neuron15 843 – 856). We are reporting a study of the effects of contrast intensity and contrast polarity on these contextual effects. Thin subthreshold lines, not detectable on a plain background, were flashed at a position collinear with a context line of varying luminance and polarity. A temporal 2AFC procedure was used to determine detection thresholds. The mere presence of a collinear context line of weak contrast, regardless of its polarity, was found to make the subthreshold lines detectable. For target lines and context lines of the same contrast polarity, increasing context contrast first enhances, then diminishes, target detectability. For target lines and context lines of opposite contrast polarity, increasing context contrast enhances target detectability. These preliminary results indicate that contrast intensity and relative contrast polarity interact in the genesis of grouping effects or contextual effects at early stages of visual processing.

scholarly journals Differential roles of contrast polarity reveal two streams of second-order visual processing

2007 ◽  
Vol 47 (15) ◽  
pp. 2047-2054 ◽  
Author(s):  
Isamu Motoyoshi ◽  
Frederick A.A. Kingdom
Keyword(s):  
Visual Processing ◽  
Second Order ◽  
Contrast Polarity

Impact of the 2019 Novel Coronavirus (COVID-19) Pandemic on OT Practitioners

2021 ◽  
Vol 75 (Supplement_2) ◽  
pp. 7512505104p1-7512505104p1
Author(s):  
Nicole Kuhl ◽  
Sara P. Johnston ◽  
David Plutschack
Keyword(s):  
Professional Practice ◽  
Professional Ethics ◽  
Signs And Symptoms ◽  
Professional Burnout ◽  
Short Term ◽  
Preliminary Results ◽  
Early Stages ◽  
Novel Coronavirus ◽  
Primary Author

Abstract Date Presented 04/13/21 This study explored OT practitioners' experiences during the early stages of the 2019 coronavirus pandemic. Preliminary results showed that participants were working with infected patients, reported increased signs and symptoms of professional burnout, and professional ethics were or may have been compromised. More research is needed to determine if the results of this study are short term or will be an ongoing issue in professional practice as the pandemic progresses. Primary Author and Speaker: Nicole Kuhl Contributing Authors: Lisa Connor, Marjorie Nicholas

scholarly journals Tetrapyrrole biosynthesis:N-methyl-N′-nitrosoguanidine-induced mutants ofPropionibacterium shermanii

1976 ◽  
Vol 28 (1) ◽  
pp. 93-100 ◽  
Author(s):  
N. H. Georgopapadakou ◽  
J. Petrillo ◽  
A. I. Scott ◽  
B. Low
Keyword(s):  
Tetrapyrrole Biosynthesis ◽  
Isolation Method ◽  
Preliminary Results ◽  
Replica Plating ◽  
Early Stages ◽  
Induced Mutants ◽  
And Control

SUMMARYAn isolation method forN-methyl-N′-nitrosoguanidine-induced catalase negative mutants ofP. shermaniibased on replica plating is described. In contrast to previous methods, it extends to the early stages of tetrapyrrole biosynthesis which are common in both corrins and porphyrins. It may thus aid in elucidating the mechanism and control of porphyrin and corrin biosynthesis. Some preliminary results are discussed.

scholarly journals Glass Patterns: Some Contrast Effects Re-Evaluated

Perception ◽  
1997 ◽  
Vol 26 (3) ◽  
pp. 253-268 ◽  
Author(s):  
Steven C Dakin
Keyword(s):  
Spatial Filtering ◽  
Contrast Effects ◽  
Visual Grouping ◽  
Relative Contrast ◽  
Low Pass ◽  
Band Pass ◽  
Opposite Contrast ◽  
Low Pass Filters ◽  
Glass Patterns ◽  
High Pass

The relative contrast of features is known to be important in determining if they can be grouped. Two manipulations of feature contrast have previously been used to criticise models of visual grouping based on spatial filtering: high-pass filtering and reversal of contrast polarity. The effects of these manipulations are considered in the context of the perception of Glass patterns. It is shown that high-pass filtering elements, whilst destroying structure in the output of low-pass filters, do not significantly disrupt the output of locally band-pass filters. The finding that subjects can perceive structure in Glass patterns composed of high-pass features therefore offers no evidence against such spatial filtering mechanisms. Band-pass filtering models are shown to explain the rotation of perceived structure in Glass patterns composed of opposite contrast features. However, structure is correctly perceived in patterns composed of two ‘interleaved’ opposite contrast patterns, which is problematic for oriented filtering mechanisms. Two possible explanations are considered: nonlinear contrast transduction prior to filtering, and integration of local orientation estimates from first-order and second-order mechanisms.

Factors characterising the maturity of BPR programmes

2003 ◽  
Vol 23 (6) ◽  
pp. 596-624 ◽  
Author(s):  
R.S. Maull ◽  
D.R. Tranfield ◽  
W. Maull
Keyword(s):  
Factor Analysis ◽  
Business Process ◽  
Quantitative Data ◽  
Implementation Strategy ◽  
Improve Performance ◽  
Public And Private ◽  
Preliminary Results ◽  
Early Stages ◽  
Strategy Process ◽  
Research Questions

Addresses the implementation of business process re‐engineering (BPR) programmes in 33 public and private organisations wishing to improve performance. By reviewing the existing literature, the research presented here began by identifying ten dimensions along which BPR projects might be measured. This research then uses these dimensions to investigate two research questions. Uses factor analysis based on quantitative data to address these questions. The factor analysis identified three independent aspects of BPR implementation: strategy, process and cost. These terms were then used in labelling three characteristic approaches, strategic BPR, process‐focused BPR and cost‐focused BPR. To investigate causality we re‐visited seven of the original organisations which had been in the early stages of implementation. Preliminary results indicate that managers might avoid the naturalistic tendency towards slow or stalled BPR maturity by intervening in a strategic sense at an earlier stage of implementation, thus bringing an organisation to a mature BPR programme more quickly.

Self-Organization of Binocular Disparity Tuning by Reciprocal Corticogeniculate Interactions

1998 ◽  
Vol 10 (2) ◽  
pp. 199-215 ◽  
Author(s):  
Alexander Grunewald ◽  
Stephen Grossberg
Keyword(s):  
Learning Process ◽  
Visual Processing ◽  
Neural Model ◽  
Image Features ◽  
Cortical Cells ◽  
Simple Cells ◽  
Complex Cells ◽  
Matching Process ◽  
Tuning Width ◽  
Opposite Contrast

This article develops a neural model of how sharp disparity tuning can arise through experience-dependent development of cortical complex cells. This learning process clarifies how complex cells can binocularly match left and right eye image features with the same contrast polarity, yet also pool signals with opposite contrast polarities. Antagonistic rebounds between LGN ON and OFF cells and cortical simple cells sensitive to opposite contrast polarities enable anticorrelated simple cells to learn to activate a shared set of complex cells. Feedback from binocularly tuned cortical cells to monocular LGN cells is proposed to carry out a matching process that dynamically stabilizes the learning process. This feedback represents a type of matching process that is elaborated at higher visual processing areas into a volitionally controllable type of attention. We show stable learning when both of these properties hold. Learning adjusts the initially coarsely tuned disparity preference to match the disparities present in the environment, and the tuning width decreases to yield high disparity selectivity, which enables the model to quickly detect image disparities. Learning is impaired in the absence of either antagonistic rebounds or corticogeniculate feedback. The model also helps to explain psychophysical and neurobiological data about adult 3-D vision.

scholarly journals Binocular Capture: The effects of mismatched Spatial frequency and opposite contrast polarity

2010 ◽  
Vol 10 (7) ◽  
pp. 368-368
Author(s):  
A. Raghunandan ◽  
S. Andrus ◽  
L. Nennig
Keyword(s):  
Spatial Frequency ◽  
Contrast Polarity ◽  
Opposite Contrast

scholarly journals Altering sensorimotor simulation impacts early stages of facial expression processing depending on individual differences in alexithymic traits

2021 ◽  
Author(s):  
Arianna Schiano Lomoriello ◽  
Antonio Maffei ◽  
Sabrina Brigadoi ◽  
Paola Sessa
Keyword(s):  
Facial Expression ◽  
Facial Expressions ◽  
Visual Processing ◽  
Event Related Potentials ◽  
Simulation Models ◽  
Facial Mimicry ◽  
Early Stages ◽  
Related Potentials ◽  
Low Levels ◽  
Expression Processing

Simulation models of facial expressions suggest that posterior visual areas and brain areas underpinning sensorimotor simulations might interact to improve facial expression processing. According to these models, facial mimicry, a manifestation of sensorimotor simulation, may contribute to the visual processing of facial expressions by influencing early stages. The aim of this study was to assess whether and how sensorimotor simulation influences early stages of face processing, also investigating its relationship with alexithymic traits given that previous studies have suggested that individuals with high levels of alexithymic traits (vs. individuals with low levels of alexithymic traits) tend to use sensorimotor simulation to a lesser extent. We monitored P1 and N170 ERP components of the event-related potentials (ERP) in participants performing a fine discrimination task of facial expressions and animals, as a control condition. In half of the experiment, participants could freely use their facial mimicry whereas in the other half they had their facial mimicry blocked by a gel. Our results revealed that only individuals with lower compared to high alexithymic traits showed a larger modulation of the P1 amplitude as a function of the mimicry manipulation selectively for facial expressions (but not for animals), while we did not observe any modulation of the N170. Given the null results at the behavioural level, we interpreted the P1 modulation as compensative visual processing in individuals with low levels of alexithymia under conditions of interference on the sensorimotor processing, providing a preliminary evidence in favor of sensorimotor simulation models.

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