Linking perceived to physical contrast: Comparing results from discrimination and difference-scaling experiments

Area of Science:

• Visual neuroscience
• Psychophysics
• Computational vision

Background:

• Understanding visual signal transformation is crucial for studying perception.
• Psychophysical methods quantify the relationship between physical stimulus intensity and perceived intensity.
• Nonlinear transformations occur within visual pathways.

Purpose of the Study:

• To investigate how stimulus contrast is encoded in human achromatic and chromatic visual pathways.
• To compare contrast encoding using contrast discrimination and maximum likelihood difference scaling (MLDS) methods.
• To model the internal representation of contrast, including transducer functions and internal noise.

Main Methods:

• Employed simple grating stimuli to assess visual contrast encoding.
• Utilized contrast discrimination (increment detection on pedestals) and MLDS approaches.
• Developed computational models with transducer functions and internal noise estimates.

Main Results:

• Transducer functions showed similar forms across experiments but varied in physical contrast range due to sensitivity differences.
• Suprathreshold chromatic and achromatic contrast processing appear similar when contrast sensitivity is accounted for.
• MLDS experiments yielded higher internal noise estimates than discrimination experiments, likely due to task complexity.

Conclusions:

• Findings support the similarity of suprathreshold chromatic and achromatic contrast processing.
• The MLDS model with constant internal noise adequately explains the data.
• Task complexity influences perceived internal noise levels in psychophysical tasks.