Why doesn't 'phase=0.5' work in grating with sqrXsqr?

Builder
1

I use grating with tex=“sqrXsqr”.
Spatial Frequency=2.5.
The result with Phase=0.5 is same as the one with Phase=0.0.
The result with Phase=0.25 is same as the one with Phase=0.75.
The one with Phase 0.0 is different from the one with Phase=0.25.

3

Hi,

The phase=0.5 with the sqrXsqr texture in PsychoPy’s grating stimulus produces a result that seems identical to phase=0.0 because of how the grating stimulus interprets phase shifts for this texture. Specifically, while one might assume that phase=0.5 would generate a different pattern, it actually adjusts the checkerboard pattern so that its orientation looks the same as phase=0.0. This effect is not only due to the checkerboard’s inherent discrete nature, but more from the interaction between the texture’s periodicity and the phase value.

Hope this helps,

Thomas