![]() ![]() ![]() They suggest that the use of SDT-based methods is preferable and that this might yield different results with the changes in thresholds not being significantly different from those predicted by probability summation. ![]() ![]() Analysis of their data demonstrated the curved prediction of signal detection theory (SDT) was significantly better at describing their data than the straight line prediction of HTT, indicating that the HTT model typically used in RF pattern analysis is not appropriate for this task. They collected observer responses when modulation was applied to either a single RF pattern or instead was distributed across four RF patterns (quad RF) having observers rate detectability on a four-level scale (confident present, probably present, probably absent, confident absent) and then subsequently plotted receiver operating characteristic curves. ( 2016) has suggested the method used in the generation of probability summation estimates based on HTT is inappropriate and may have resulted in incorrect conclusions being drawn in these earlier papers. They found that observer thresholds for detecting the presence of modulation decreased faster than was predicted by probability summation (PS the increased chance of detection of local features due to an increase in the number of local elements available to detect) when modeled under high threshold theory (HTT Loffler et al., 2003) and concluded there was evidence of integration around the contour (global processing) of these shapes when there were fewer than eight cycles of modulation (Loffler et al., 2003).Ī recent study by Baldwin et al. Previous studies interested in the visual system's ability to globally integrate shape information using RF patterns have examined the effect of varying the number of complete cycles of modulation on the RF pattern while the wavelength remains the same (see Figure 1 Dickinson, Bell, & Badcock, 2013 Dickinson, Cribb, Riddell, & Badcock, 2015 Dickinson, McGinty, Webster, & Badcock, 2012 Loffler, Wilson, & Wilkinson, 2003 Schmidtmann, Kennedy, Orbach, & Loffler, 2012 Tan, Dickinson, & Badcock, 2013). The results provide further evidence for the global processing of random-phase RF patterns and indicate that RF patterns and modulated lines are processed differently. They also show no evidence of global integration with modulated line stimuli. The results indicate global processing of random-phase RF patterns and evidence for an interaction between local and global cues for fixed-phase RF patterns. Thresholds were collected from eight naïve observers and compared to probability summation estimates calculated using methods derived from both high threshold theory and signal detection theory. The current study investigates these claims using fixed-phase (in which the local elements have spatial certainty) and random-phase (in which the local elements have spatial uncertainty) RF patterns and modulated lines. Furthermore, it has been argued that RF patterns and lines are processed in a similar manner (Mullen, Beaudot, & Ivanov, 2011 Schmidtmann & Kingdom, 2017). They could not distinguish between global integration and probability summation. More recently, this conclusion has been questioned by researchers using a method of calculating probability summation derived from signal detection theory (Baldwin, Schmidtmann, Kingdom, & Hess, 2016). On finding that the rapid improvement in sensitivity to deformation as more cycles of modulation were added was greater than expected from probability summation across sets of local independent detectors, they concluded that global integration of contour information was occurring. Previously, researchers have used circular contours with sinusoidal deformations of the radius (radial frequency patterns) to investigate the underlying processing involved in simple shape perception. ![]()
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