diff --git a/iblrig_tasks/_iblrig_tasks_ephysChoiceWorld/task_parameters.yaml b/iblrig_tasks/_iblrig_tasks_ephysChoiceWorld/task_parameters.yaml
new file mode 100644
index 000000000..b437396e8
--- /dev/null
+++ b/iblrig_tasks/_iblrig_tasks_ephysChoiceWorld/task_parameters.yaml
@@ -0,0 +1 @@
+'CONTRAST_SET_PROBABILITY_TYPE': skew_zero  # uniform or skew_zero: uniform makes the 0 contrast as likely as the others, while skew_zero makes it half as likely as other contrasts