Global orientation estimation in noisy conditions

The present paper studies the perceived orientation of line patterns with variable elongation, line length, orientation jitter, and presentation time. It evaluates whether the internal noise and sampling efficiency evaluated by equivalent noise paradigm (Pelli 1981) depend on the spatial configuration and temporal characteristics of the stimulation. The evaluated internal noise was compared to the results of double-pass noise estimation. In addition, the eye movements of the participants during active exploration of the line patterns were recorded and analyzed with respect to the stimulus characteristics. The results indicate the presence of late internal noise and show that the internal noise and sampling efficiency strongly depend on the elongation, duration and line length of the patterns. The response time increases with the orientation jitter and with the variability in line length of the patterns. It is longer also near the reference orientation for the low levels of added external noise. These results contradict some of the major assumptions of the variance-summation model and question its applicability in characterizing the perceived orientation of multi-element patterns.