Question

why did the rats press the lever more often when presented with the combination of nicotine and visual cues?
oa. the visual cues are an indication that other drugs will soon follow.
ob. a rats visual sense is more sensitive than any of its other senses.
oc. nicotine is believed to enhance the power of the visual cues.
od. the visual cues were a green light, which the rats had previously associated with ingesting cocaine.

Explanation:

In behavioral - related studies, rats can form associations between stimuli. When nicotine is combined with visual cues, if the visual cues have been previously associated with a rewarding experience (like ingesting cocaine), the rats will press the lever more often due to the learned association. Option a has no basis as there is no indication other drugs will follow. Option b about visual sense sensitivity is not relevant to the lever - pressing behavior in this context. Option c has no evidence that nicotine enhances visual cues' power in this way. Option d provides a valid association that can drive the behavior.

Answer:

D. The visual cues were a green light, which the rats had previously associated with ingesting cocaine.