Is the S-opponent chromatic sub-system sluggish?

Area of Science:

• Visual neuroscience
• Human psychophysics
• Color vision

Background:

• The S-opponent pathway is widely believed to be slower than the L/M-opponent pathway.
• Previous research suggests S-opponent signals in Macaque V1 are available 96-135 ms post-stimulus, while L/M-opponent signals appear at 68-95 ms.

Purpose of the Study:

• To psychophysically investigate the latency difference between S-opponent and L/M-opponent visual pathways.
• To determine if the claimed significant latency difference between these pathways is observable in human perception.

Main Methods:

• Measurement of reaction times to chromatic increments (S/(L+M) and L/(L+M)).
• Empirical determination of the equiluminant plane and tritan line.
• Use of spatio-temporal luminance noise to mask luminance cues.
• Adaptive staircase method for 'go, no-go' task to estimate thresholds and reaction times.

Main Results:

• When stimuli are brief, confined to chromatic channels, and presented at equivalent threshold levels, the latency difference is significantly reduced.
• Visually triggered reaction times indicate a maximum latency difference of 20-30 ms between the L/M-opponent and S-opponent sub-systems.

Conclusions:

• The perceived latency difference between S-opponent and L/M-opponent pathways is much smaller than previously reported.
• These findings challenge the notion of a sluggish S-opponent pathway in human color vision.