David H. Peterzell^1,2 (), Omar Bachtoula³, Ichasus Llamas-Cornejo³, Ignacio Serrano-Pedraza³; ¹Fielding Graduate University, Santa Barbara, California, ²JFK School of Psychology, National University, Pleasant Hill, California, ³Department of Experimental Psychology. Faculty of Psychology. Complutense University of Madrid, Madrid, Spain

Orientation selectivity for luminance-varying patterns is well-supported by anatomical, physiological, and psychophysical studies. Most psychophysical evidence has come from subthreshold summation, adaptation, and masking experiments, which suggest the existence of narrowly tuned orientation mechanisms with bandwidths ranging from 6° to 30°. In this study, we used factor-analytic dimension reduction techniques to investigate the presence of independent orientation mechanisms. Using Bayesian staircases, 36 participants performed a contrast detection task with gratings of 1.5 c/deg at ten orientations (0° to 90°), spatially windowed by a Butterworth 2D function with a diameter of 11°. Preliminary results revealed no significant differences in contrast thresholds across orientations. Instead, contrast thresholds exhibited strong intercorrelations, suggesting the presence of a broadly tuned factor or factors mediating sensitivity across orientations. A two-factor analysis (PCA with oblique Promax rotation) identified two highly intercorrelated factors: one peaking at vertical-to-oblique gratings (F1: 0° to ~50°) and the other at oblique-to-horizontal gratings (F2: ~50° to 90°). These findings are consistent with the presence of broad orientation-tuning mechanisms but do not support the existence of independent, narrowly tuned mechanisms. Split-half and test-retest analyses replicated these results, although test-retest reliability was not robust. More broadly, these findings challenge the traditional view that contrast sensitivity is determined by narrowly tuned, independent orientation-selective mechanisms. Instead, they support the idea that orientation and spatial frequency sensitivity are mediated by overlapping, interdependent mechanisms with broad tuning. However, the limited sample size and moderate reliability highlight the need for caution in interpreting these results. Future research with larger samples and enhanced reliability testing is essential to validate and extend these findings.

Acknowledgements: Supported by grant PDI2021-122245NB-I00 from Ministerio de Ciencia e Innovación (Spain) to ISP