1,720,970 research outputs found
Typical development of Motion perception and Form discrimination abilities in children
No full textVisual functions have been widely investigated in patients with developmental
disorders. This study aims to analyze the development of dorsal
and ventral visual function in children with typical development, measured
as motion and form discrimination abilities. A sample of 304 children
(age: 4-12 years; 154 males) participated in the experiment. Non-verbal
intelligence (Raven’s matrices), visual acuity (Lea test), motion perception
(motion coherence test-MCT) and form recognition (form coherence
test-FCT) were assessed. The MCT consists of 150 white dots on a black
background moving coherently at a constant velocity in one of the eight
directions (signal) or in a Brownian manner (noise). The task was to recognize
the direction of the signal dots. The FCT consists of white dots (signal)
composing one of eight possible forms through spatial alignment of the
dots, the noise was created by non-aligned dots distorting the form. The
task was to recognize the form. Difficulty was increased by reducing the
dot coherence (signal/noise) from 100% (no noise) to 36% in five levels.
MANOVA showed a significant increment of motion and form perception
accuracy with age, steeper for form as compared to motion recognition.
Both functions are influenced by noise but motion discrimination seemed
to be less affected. While noise had a stronger effect on the younger children
in the FCT (worse performance with noise in the youngest) no such
age effect was found in MCT. Motion and form perception are related
to general intelligence at different ages as well as to the visual acuity.
These results confirm the slowness in development of dorsal function
as compared to ventral function. Visuo-spatial attention, general intelligence
and visual acuity mediate the visual functionality development
The Effect of Luminance Condition on Form, Form-from-Motion and Motion Perception
Full text linkThis study investigated to what extent rod-dominated vision affects motion and form perception accuracy. Twenty-nine healthy subjects took part in the experiment. Form coherence (FC), form-from-motion (FFM) and motion coherence (MC) tests were assessed in low-light (rod-dominated vision) and high-light (cone-dominated vision) conditions. For each test we determined the accuracy by evaluating the correct detection obtained in five levels of coherence (corresponding to different signal-to-noise ratio). The results evidenced that motion, form and form-from-motion accuracy decreased in low-light condition. Furthermore, light condition effect was differently mediated by noise according to the type of task. The motion perception is affected only at high noise levels, while form discrimination was globally affected at all the levels, also in absence of noise, both for static (FC) and dynamic stimuli (FFM). We conclude that in rod-dominated vision form-from-motion perception is more defected than form and motion perception. We hypothesized that our results are due to the integration between M and P cells in FFM test increases the form perception accuracy in high-light condition but this advantage is completely lost during low-light condition, when the rods need to integrate information both from M and P cells
Motion perception, form discrimination and visual motor integration abilities in mTBI patients
No full textMotion-from-Form perception in Scotopic and in Photopic light conditions
No full textHuman visual perception is globally worsened under dim light condition.
The aim of this study was to investigate how rod-dominated vision
affects motion perception in a motion-from-form (MFF) and motion coherence
(MC) task. Thirty healthy subjects (11 males, mean age 21.3 years)
participated in the experiment. MFF and MC were tested both in scotopic
and photopic light conditions. Both the MFF and MC stimuli consisted of
nine empty circles moving coherently at a constant velocity of 10.7°/sec
in one of eight directions (cardinal and oblique). Five noise-levels were
used: starting from zero, the noise increased by 6 units in each following
level. In the MFF test 169 empty white squares acted as stationary background.
Nine target-stimuli were drawn in place of the same number
of squares. To make the shape appear to move, in the subsequent frame
each target-stimulus reverted to square while the next square changed
to circle, following a specific direction. The noise consisted of circle positioned
randomly in the space, irrespectively to their previous position. In
the MC test the target-stimuli moved coherently on a black background
and the noise was obtained by stimuli moving in a Brownian manner. The
subjects had to identify the directions of the coherent motion in both tests.
The accuracy was evaluated for each condition. ANOVA showed a significant
global effect of light condition, evidencing disrupted performances
in rod-dominated vision, significant differences between the types of stimuli
(lower scores in MFF as compared to MC) and a significant interaction
stimuli type by light condition. In conclusion, the results confirm that in
scotopic light levels motion perception is not significantly altered using
MC, while it is degraded in higher order motion stimuli, such as MFF
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
