Chromatic contrast in luminance-defined images affects performance and neural activity during a shape classification...

Area of Science:

• Visual perception
• Cognitive neuroscience
• Electrophysiology

Background:

• Object recognition models often prioritize luminance-defined shape.
• The interplay between color (chromatic) and luminance signals in form processing remains unclear.

Purpose of the Study:

• To investigate the role of chromatic contrast in object shape processing.
• To assess the impact of color signals on the temporal dynamics of shape perception using electroencephalography (EEG).

Main Methods:

• Participants classified Gaborized shapes under varying chromatic and luminance contrast conditions.
• Event-related potentials (ERPs), including the N1 and Late Positive Potential (LPP), were recorded.
• Stimuli varied in excitation of luminance (L+M), L-M, and S-(L+M) channels at different intensity thresholds.

Main Results:

• At threshold, classification accuracy and early ERPs (N1) were similar across conditions.
• Above threshold, objects with combined chromatic and luminance information showed poorer performance and reduced N1 amplitude.
• Shape sensitivity was more pronounced in the LPP component, with S-(L+M) contrast causing a sustained amplitude shift.

Conclusions:

• Shape classification depends on both chromatic and luminance image content.
• Chromatic contrast significantly influences the time course of shape processing, affecting both early perceptual and later cognitive ERP components.
• This study provides comprehensive evidence from behavioral and electrophysiological measures for the combined role of color and luminance in object recognition.