![]() Observer thresholds significantly lower than probability summation estimates were concluded to demonstrate evidence for integration of information. One method these studies used to determine whether there was evidence for integration of contour information was the comparison of observer thresholds to those predicted by probability summation. One of the primary conclusions about RF patterns in previous studies was that contour information was integrated around the pattern when the RF number was less than 10 ( Bell, Dickinson, & Badcock, 2008 Dickinson, Almeida, Bell, & Badcock, 2010 Dickinson, McGinty, Webster, & Badcock, 2012 Hess, Wang, & Dakin, 1999 Loffler, Wilson, & Wilkinson, 2003 Schmidtmann, Kennedy, Orbach, & Loffler, 2012 Tan, Dickinson, & Badcock, 2013). Similar to how a Gabor pattern is useful for studying the early visual pathway, RF patterns are useful for examining factors which effect “mid-level” human vision. Although RF patterns do not describe all shapes necessary for object recognition (see Schmidtmann & Fruend, 2019), RF patterns are stimuli which can be used to increase our understanding of how contour information is integrated within the visual pathway. Comparing the results for patterns with differing cycles of modulation researchers drew various conclusions about the perception of RF patterns and, more generally, mid-level visual processes. Thus, previous research modified the amplitude of the sine wave/s to find observer thresholds for a fixed number of sine waves (or cycles of modulation) around a pattern. increasing RF number or number of cycles) increases the discriminability of the pattern. Increasing the amplitude of the sine wave or the number of sine waves present on the pattern (i.e. Changing the radial frequency (RF number) changes the number of complete sine waves which can fit around the pattern. An RF pattern ( Wilkinson, Wilson, & Habak, 1998) is a circle with a radius which has been modified by one or more sine waves as a function of polar angle. ![]() One pattern which has been useful in the study of simple shape perception has been the radial frequency (RF) pattern. The perception of part or whole simple shapes by the visual system is thought to be a mid-level process ( Merigan, 1996 Pasupathy & Connor, 2002 Yau, Pasupathy, Brincat, & Connor, 2013) in the feed forward hierarchy of human vision ( Van Essen, Anderson, & Felleman, 1992). These differences in gaze patterns are likely driven by the underlying local or global processing of the fixed or random phase single cycle patterns, respectively. It was also found that for the single cycle patterns observers tended to fixate on different locations on the pattern: on the maximum orientation difference from circular for the fixed phase pattern and on the point of maximum curvature for the random phase pattern. This strategy had a significant effect on observer thresholds for the fixed phase single cycle condition, with greater adherence to the strategy resulting in lower thresholds. The results showed that observers fixated on the known location of deformation for the fixed phase single cycle condition but used a more central fixation for the other three conditions. This study compared fixation patterns across four conditions: fixed phase single cycle random phase single cycle fixed phase three cycle and random phase three cycle RF3 patterns. However, the effect of fixed and random orientation (phase) on observer gaze strategies used to discriminate RF patterns has not been directly tested. Typically, these patterns have been presented in a random orientation from trial-to-trial in order to maintain spatial uncertainty as to the location of the deformation on the pattern, as it may affect observer strategy and performance. Radial frequency (RF) patterns, circles which have had their radius modulated as a function of their polar angle, have been used in the examination of the integration of contour information around closed contour patterns.
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