228
given (p. 433) and thus also when a shift in strategy is required in order to
execute an intention (p. 437).
In birds the situation has not been so intensively studied. Lesion damage
to the hippocampus and the neighbouring accessory hyperstriatal areas does
not affect simple discriminations (Hodos et al., 1973). But there are deficits
on a pattern discrimination reversal (Stettner and Schultz, 1967). Examina-
tion of these results has led to the suggestion that the Iesioned birds had an
impaired ability to shift attention between aspects of the stimulus complex
(Cohen, 1967; Stettner, 1974). There is some consensus that this area func-
tions in the control of orientation to aspects of a stimulus (Salzen and Parker,
1975; Gentle et al., 1978).
Oades (1976a) has shown that lesions to the dorsomedial hyperstriatum
and putative hippocampus in chickens decrease distractability on a runway
task and incur behavioural deficits (e.g. passive avoidance) that parallel the
behavioural deficits produced by hippocampal lesions in mammals. In an
examination of the mechanism that might be affected by these lesions, Oades
(1976b) showed that when faced by an array of red and yellow food grains
and pebbles, the brain-damaged birds were less distracted by the pebbles than
were the controls. Further the birds showed a persistence in the use of -stra-
tegies for selecting a particular colour of food grain whilst feeding. Thus it
seems that lesions can affect the shifting of attention and the use of learned
specifications in the control of a search strategy. Attentional mechanisms in-
clude not only the selection of stimuli but their matching with learned speci-
fications (e.g. recognition, cf. Broadbent, 1970).
There is further reason to suppose that processes, related to those for learn-
ing and retrieval, take place in the dorso-medial area. Lesions in the dorsal
midline, rather than in the lateral hyperstriatum or neostriatum impair the
ability of nutcrackers (Nucifraga caryocatactes) to find the places where they
have stored food (Krushinskaya, 1966).
This current study addresses three questions.
(1) If attentional processes are damaged by limbic lesions they would not
be expected to be restricted to the visual modality: does damage to the avian
putative hippocampal complex affect performance on auditory tasks? Until
recently it could be said only that some auditory responses may be record-
able from the hyperstriatum (Adamo and King, 1967) and that damage here
can affect orientation of the head to auditory stimuli (Adamo and Bennett,
1967).
(2) The putative hippocampus of birds may cover several functional sub-
areas. Are there separable effects that result from non-overlapping lesions plac-
ed anterior and posterior to the anterior commissure on the performance of
an auditory recognition task? The presence of acetyl choline is a character-
istic of the mammalian hippocampus. Staining for acetyl cholinesterase in the
forebrain of pigeons (B. Srebro, personal communication, 1978) suggests
that the putative hippocampal area extends further posterior than the area
anterior to the anterior commissure and dorsal to the septum described for