In the introduction, we distinguished 3 types of attributes of
food reward delivery: its intrinsic incentive value, its intrinsically
neutral sensory features, and the reactions that the neutral
features evoke in the animal because of their association in
memory with the intrinsic incentive value, The learned auditory
and visual secondary reinforcers we have used are similar to
each other in lacking intrinsic incentive value (the first of these
types of attribute). Also, they are both associated in memory
with primary reinforcement and in the normal animal evoke
reactions (the third type of attribute) because of this association.
The difference between them is in their intrinsically neutral
sensory properties (the second type of attribute). One of them
is in the same modality as the discriminative stimuli and in the
same spatial location, the other is not. For this reason, as explained
in the introduction, associations between the discriminative
stimuli and the sensory features of the secondary reinforcer
may be expected to be facilitated by the visual secondary
reinforcer, as compared with the auditory secondary reinforcer.
Therefore, from the fact that bilateral amygdalectomy had far
less effect on learning for the visual than for the auditory secondary
reinforcer (Fig. 4), we conclude that the sensory-sensory
association, between a visual discriminative stimulus and the
visual properties of a spatially contiguous reinforcer, is independent
of the amygdala.