make decision about replacing image set A with a more balanced stimulus set

[matchings]

image set A, aka the training set, has several images with low detectability. This leads to the concern that any differences in physiology (such as a difference in responsiveness) between image set A and image set B could be due to differences in detectability and associated behavior (such as differences in reaction times). It is desirable for image set A and image set B to have similar overall patterns of detectability, and for them to both be selected in a similar, principled way (rather than manual selection as is the case for set A).

Making this change requires mice to start training on a different regimen and thus is non-trivial and must be done carefully at the right time.