scholarly journals Negative Slope Coefficient: A Measure to Characterize Genetic Programming Fitness Landscapes

2006 ◽  
pp. 178-189 ◽  
Author(s):  
Leonardo Vanneschi ◽  
Marco Tomassini ◽  
Philippe Collard ◽  
Sébastien Vérel
Keyword(s):  
Genetic Programming ◽  
Fitness Landscapes ◽  
Negative Slope ◽  
Slope Coefficient

A Study of Fitness Distance Correlation as a Difficulty Measure in Genetic Programming

2005 ◽  
Vol 13 (2) ◽  
pp. 213-239 ◽  
Author(s):  
Marco Tomassini ◽  
Leonardo Vanneschi ◽  
Philippe Collard ◽  
Manuel Clergue
Keyword(s):  
Genetic Programming ◽  
Statistical Study ◽  
Fitness Landscapes ◽  
Distance Correlation ◽  
Fitness Distance Correlation

We present an approach to genetic programming difficulty based on a statistical study of program fitness landscapes. The fitness distance correlation is used as an indicator of problem hardness and we empirically show that such a statistic is adequate in nearly all cases studied here. However, fitness distance correlation has some known problems and these are investigated by constructing an artificial landscape for which the correlation gives contradictory indications. Although our results confirm the usefulness of fitness distance correlation, we point out its shortcomings and give some hints for improvement in assessing problem hardness in genetic programming.

scholarly journals BOLD signal response in primary visual cortex to flickering checkerboard increases with stimulus temporal frequency in older adults

PLoS ONE ◽  
2021 ◽  
Vol 16 (11) ◽  
pp. e0259243
Author(s):  
Yuji Uchiyama ◽  
Hiroyuki Sakai ◽  
Takafumi Ando ◽  
Atsumichi Tachibana ◽  
Norihiro Sadato
Keyword(s):  
Older Adults ◽  
Visual Cortex ◽  
Primary Visual Cortex ◽  
Visual Stimulus ◽  
Temporal Frequency ◽  
Group Analysis ◽  
Negative Slope ◽  
Slope Coefficient ◽  
Response Change ◽  
Fmri Analysis

Many older adults have difficulty seeing brief visual stimuli which younger adults can easily recognize. The primary visual cortex (V1) may induce this difficulty. However, in neuroimaging studies, the V1 response change to the increase of temporal frequency of visual stimulus in older adults was unclear. Here we investigated the association between the temporal frequency of flickering stimuli and the BOLD activity within V1 in older adults, using surface-based fMRI analysis. The fMRI data from 29 healthy older participants stimulated by contrast-reversing checkerboard at temporal flicker frequencies of 2, 4, and 8 Hz were obtained. The participants also performed a useful field of view (UFOV) test. The slope coefficient of BOLD activity regarding the temporal frequency of the visual stimulus averaged within V1 regions of interest was positive and significantly different from zero. Group analysis in the V1 showed significant clusters with positive slope and no significant clusters with a negative slope. The correlation coefficient between the slope coefficient and UFOV performance was not significant. The results indicated that V1 BOLD response to a flickering visual stimulus increases as the stimulus temporal frequency increases from 2 to 8 Hz in older adults.

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