Contrast amplification in global texture orientation discrimination

Lawrence G. Appelbaum, Zhong-Lin Lu, George Sperling
2007 Journal of Vision  
We show that adding a low-contrast texture stimulus that is far below its own detection threshold to an ambiguously oriented high-contrast texture can produce an easily perceived global orientation. When such a low-contrast (e.g., 0.1%) test texture and a high-contrast (e.g., 2%) amplifier texture are interleaved, the effective strength for global orientation detection closely approximates the product of the two contrasts. Therefore, adding two ambiguous textures, an amplifier texture at 5Â its
more » ... threshold contrast for global orientation discrimination and a test texture at 1/5Â its threshold contrast, produces threshold global orientation discrimination, that is, 5Â amplification of the below-threshold test texture. The observed 5Â amplification factors are larger than facilitation effects reported in other pattern tasks. Amplification is 11Â when orientation discrimination thresholds are compared to absolute detection thresholds. For second-order textures, maximum contrast amplification is about 2.5Â. A contrast gain control model is presented that accounts for 90% of the variance in observed dVfor texture patterns of differing geometries, exposure durations, and component contrasts. In the model, very low-contrast orientations are represented by power functions of their contrasts, with an exponent greater than two. As the contrast of an amplifier texture increases beyond about 4%, feedforward gain control exerted by the amplifier ultimately nullifies the amplification effect and produces masking.
doi:10.1167/7.10.13 pmid:17997682 fatcat:2kf62os3zrhsvhosvhht2klwfe