Abstract
Sensitivity to luminance difference, or contrast sensitivity, is critical for animals to survive in and interact with the external world. The contrast sensitivity function (CSF), which measures visual sensitivity to spatial patterns over a wide range of spatial frequencies, provides a comprehensive characterization of the visual system. Despite its popularity and significance in both basic research and clinical practice, it hasn’t been clear what determines the CSF and how the factors underlying the CSF change in different conditions. In the current study, we applied the external noise method and perceptual template model to a wide range of external noise and spatial frequency (SF) conditions, and evaluated how the various sources of observer inefficiency changed with SF and determined the limiting factors underlying the CSF. We found that only internal additive noise and template gain changed significantly with SF, while the transducer non-linearity and coefficient for multiplicative noise were constant. The 12-parameter model provided a very good account of all the data in the 200 tested conditions (86.5%, 86.2%, 89.5%, and 96.4% for the four subjects, respectively). Our results suggest a re-consideration of the popular spatial vision model that employs the CSF as the front-end filter and constant internal additive noise across spatial frequencies. The study will also be of interest to scientists and clinicians engaged in characterizing spatial vision deficits and/or developing rehabilitation methods to restore spatial vision in clinical populations.
Highlights
Sensitivity to luminance difference, or contrast sensitivity, is critical for animals to survive in and interact with the external world, e.g. searching for food, locating water source, mating, socializing, and disclosing predators from its surrounding camouflages [1]
The pattern of results suggested that contrast threshold increased with external noise, and the rate of increase was slower in high spatial frequencies
We tested four different models: (1) the full model: all parameters are different for the 40 psychometric functions (PFs), leading to a total of 80 parameters (40 slopes and 40 thresholds); (2) reduced model 1: the slopes are the same but the thresholds are different across the PFs; (3) reduced model 2: the thresholds are the same but the slopes are different across the PFs; (4) the most reduced model: the slopes and thresholds are the same across the PFs
Summary
Sensitivity to luminance difference, or contrast sensitivity, is critical for animals to survive in and interact with the external world, e.g. searching for food, locating water source, mating, socializing, and disclosing predators from its surrounding camouflages [1]. The CSF has been found to differ greatly among species [13], improve with development [14], deteriorate with aging [15], and vary with attentional state [16,17], luminance level [18], adaptation [19], and a variety of visual diseases, including amblyopia [20,21,22], glaucoma [23,24], dyslexia [25], and major depressive disorder [26,27]. The pattern of CSF changes may vary with clinical conditions. Amblyopia is largely regarded as a high SF deficit [28,29] and dyslexia as a condition with low SF deficits ([30,31], but see [32])
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