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This chapter continues the discussion of animal discrimination learning, concentrating on the effects produced by giving the animals prior exposure to the stimuli to be discriminated. The experiments reviewed establish that such exposure facilitates subsequent discrimination. Analysis of the mechanisms involved indicates that this perceptual learning effect is multiply determined — that latent inhibition plays a role, as does the formation of associations among the various features of the pre-exposed stimuli. In addition, they suggest the operation of a further learning process that serves to boost the perceptual effectiveness of the distinctive features of the stimuli.

This chapter discusses ways in which information is stored in the brain. Memory and habituation, and the characteristics of filial imprinting are discussed. Habituation is a form of learning wherein a behavioural or physiological response to a repeatedly applied stimulus wanes if the stimulus is not associated with a reward or punishment. Filial imprinting is the process whereby young birds form an attachment to their mother or some artificial substitute.

The finding in Chapter 2 that biochemical changes are associated with imprinting supports the view that learning involves changes in neural connectivity. However, biochemical changes may be caused by a variety of factors of which learning is only one. This chapter describes three experiments aimed at controlling these factors. The possibility that biochemical changes reflect some aspect of information storage during the imprinting process was excluded by control procedures, whereas certain other explanations have been.

This chapter examines whether the whole or only some parts of the anterior of the forebrain roof is involved in the imprinting process. Changes in incorporation associated with training have been observed only in a restricted part of the forebrain roof, the hyperstriatum ventrale. The region is approximately 2.4 millimetres long and is centred approximately on the midpoint between the anterior and posterior poles of the cerebral hemispheres.

This chapter investigated whether the ‘intermediate and medial part of hyperstriatum ventrale’ (IMHV) is necessary for imprinting. The IMHV of chicks were lesioned and exposed to an imprinting stimulus. It was shown that if the IMHV is destroyed bilaterally before training, the chicks fail to develop a preference for the training object. If the region is destroyed bilaterally after training is complete, retention is severely impaired. The results suggest that the IMHV is critical for storing information having a direct influence on filial preferences.

This chapter examines the roles of the right and left IMHV in the retention of a preference. Results show a hemispheric asymmetry in the roles of the right and left IMHV in the imprinting process. The left IMHV has a storage function and may itself be a store. Under special circumstances, the left and right IMHV may be removed, but the chick retains the previously acquired preference. Based on these data, the existence of another store is proposed, referred to as S'. The store appears to be formed slowly under the control of the IMHV, which may act as a buffer store.

This chapter investigates the effects of brain lesions on imprinting; the training objects were either a rotating flashing red box or a stuffed hen jungle-fowl. In experiments, the preferences of both chicks trained on the jungle fowl and chicks trained on the red box were reduced. The effect on the box-trained chicks was significant, while the effect on chicks trained on the jungle fowl was relatively weak. The preferences of young chicks were affected by two underlying processes. There is (i) a developing predisposition which becomes apparent as an increasing preference for the jungle fowl. The predisposition can be activated by non-specific experiences, and once activated interacts with (ii) a learning process through which chicks come to recognize specific objects to which they have been exposed. The IMHV is concerned with the second process.

This chapter reviews evidence that activity in the sensory pathways is insufficient for information storage. The roles of noradrenaline and testosterone in imprinting processes are analyzed. The concentration of noradrenaline in parts of the forebrain, including the IMHV, appears to limit acquisition particularly in chicks trained on the box. For fowl-trained chicks, preference for the jungle-fowl was associated with testosterone concentration in the plasma. The results suggest that at least some of the neural mechanisms underlying the preference for the box and for the fowl, respectively, are subject to different physiological constraints.

This chapter examines whether there are morphological and physiological changes in the IMHV associated with imprinting. When chicks were trained by exposure to a rotating red box, changes were detected in neuronal activity in the IMHV. Changes in the structure of synapses in the IMHV were studied in chicks trained by exposing them to a red box or to a flashing horizontal bar rotating upwards. Synaptic structures were modified by training regardless of the stimuli used. In both cases, training was associated with increased length of the post-synaptic density of synapses on dendritic spines. Synapses in the left IMHV were affected; no significant changes were observed in the right IMHV.

This chapter discusses current knowledge about the organization of the IMHV, the kind of information to which it has access, and its influences on other parts of the brain. Topics covered include the connections of the IMHV, chemical and cellular components of the IMHV, and cerebral circuits in birds and mammals.

This chapter reviews discussions in the preceding chapters. These include memory defects resulting from lesions of the brain, particularly the medial temporal lobe and parts of the diencephalons of human subjects and macaque monkeys. These defects are compared with those of chicks with IMHV lesions. The memory needed to perform skills is distinguished from recognition memory. The relationship between imprinting and plasticity in the visual cortex of kittens is examined. The possible neural mechanisms underlying predispositions, and the way predispositions may interact with learning processes are considered in the context of species and individual recognition.