the effects of testosterone on the distractability of chicks by irrelevant and relevant novel...

Anita. Behav,, 1974, 22, 397--404

T H E E F F E C T S O F T E S T O S T E R O N E O N T H E D I S T R A C T A B I L I T Y O F

C H I C K S BY I R R E L E V A N T A N D R E L E V A N T N O V E L S T I M U L I

BY JOHN ARCHER Ethology and Neurophysiology Group, School of Biological Sciences, University of Sussex

Abstract. Young male chicks were trained to run for a food reward in a runway; half the sample were subsequently injected with testosterone oenanthate (Ts) and half with the oil vehicle only (Cs). Two days later, they were given a series of tests in the runway to investigate the effect which changing the colour or pattern of either the runway walls or the food dish had on their times to run and feed continuously. In two experiments, it was generally found that Ts showed more pronounced decreases in running times when the colour or pattern of the food dish was changed but Cs showed more pronounced decreases in running times following changes in the walls of the runway. These results supported predictions derived from the hypothesis of Andrew (1972a) that testosterone increases persistence of 'activated search specifications'. Alternative possible explanations in terms of fear, response perseveration, or attention-switching were briefly discussed, and it was concluded that these could not account for the present results and those found in related studies.

The results of several experiments carried out on young male chicks in this laboratory have revealed an effect of testosterone on behaviour which has been described as increased persistence (Andrew & Rogers 1972). This was first demon- strated in a food-search situation involving preferred and non-preferred colours of grain scattered over a pebbled background (which made careful search necessary if preferred food was to be obtained). Testosterone-treated birds (Ts) typically showed long continuous runs of pecks on their preferred type of food, whereas oil-injected controls (Cs) showed more shorter runs on both preferred and non-preferred grains (Rogers 1971; Andrew & Rogers 1972; Andrew 1972a).

In a second type of food search situation, where the pebbled background was absent, Ts showed longer runs of pecks in a particular area before moving to feed elsewhere (references cited above). This result is similar to another finding, that Ts showed longer fixation times and fewer 'scanning' head movements in a novel cage than Cs did (Archer 1973).

Further studies have shown that the changes in search behaviour occur at similar doses to the more well-documented changes in copulation and attack following testosterone treatment in male chicks (Andrew 1972b), that they do not occur in female chicks (Andrew 1972b), and that comparable effects occur following castration and replacement therapy with physiological levels of testosterone in adult fowl (Rogers, in press).

From the results of the food search tests reviewed above, Andrew (1972a) argued that

depending on the precise test situation, testosterone either increases the persistence of criteria for an acceptable match when searching for a particular type of stimulus (e.g. preferred food in the search tests on a pebbled floor), or alterna- tively it increases the persistence of specifications for a particular spatial locality (e.g. an area of the floor in the search tests on the plain floor). Thus two types of change in search behaviour were interpreted, on a post hoe basis, as increases in the same hypothetical construct, 'persistence' (Andrew 1972a, b). It was therefore considered necessary to carry out a study of testosterone and chick behaviour in a different situation from the food search tests, to test predictions which might follow from Andrew's (1972a, b) theoretical treatment.

In a detailed consideration of the evidence from search tests in relation to theories of recognition processes, Andrew (1972a) argued that the most likely basic factor underlying the changes in search behaviour was 'increased persistence of activation or availability of search specifications, once they had come into use' (pp. 193 to 195). Andrew envisaged that, in a food search situation, these 'activated search specifications' could involve both details of where food is to be expected and what food and its associated stimuli look like. Thus, if a bird with increased 'persistence' is observed in a feeding test, we should predict that it would less readily adapt to changes in the environment involving either the place of feeding (prediction 1.), or the type of food object (prediction 2), since changes in its central specifications would

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398 A N I M A L B E H A V I O U R , 22, 2

occur less readily. Thirdly, we should predict that it would show increased resistance to distraction by stimuli irrelevant to the ongoing response, since its 'presently-activated search specifications' (Andrew 1972a, p. 195), would be more stable in the face of competing inputs.

The present study investigated these three predictions using a runway response for a food reward. Chicks were first trained, then injected with testosterone (T) or oil (C), and finally tested in the runway to investigate the effect on their running times of changing either the food dish or some feature of the runway walls. These tests were interspersed with control trials during which the runway remained identical to that used during training.

The major concern of the two experiments reported here was to test predictions 2 and 3 described above, by measuring the relative distractability of T and C chicks by changes at the food dish or at other places in the runway. In this context, 'distractability' refers to the mean increase in time taken to run and feed during the trials involving a change in the runway, over the control trials.

Prediction 1, which refers to decreased readi- ness to adapt to changes in the place of feeding was investigated in experiment 2 by changing the place of the food dish but keeping it identical in form to that used on previous trials. In this case, it was predicted that Ts would pay more visits to the place where the dish had been, and would take longer to feed in the new location, than Cs would.

Experiment 1 Methods

Twenty male chicks (Warren Sex-link, South- down Hatchery, Lewes) were obtained on their second day after hatching and individually housed in cages 30 • 22.5 • 45 cm. During their first week they were trained to run a runway for a food reward (3�89 food deprivation). They received ten trials on each of days 4, 5 and 6.

The procedure on individual trials was as follows:

After 15 s in the start box (15 cm2) the chick was allowed access to the runway (25 • 120 • 37.5-cm high), and its response 'shaped' by first placing the food dish near the start box, and moving the dish forward each time the chick fed on two successive trials in under 15 s. On each trial the chick was removed by hand and replaced in the carrying box, either after it had

fed for 12 to 15 s or, if it did not feed, after 60 s from the removal of the start box door. In- tervals between trials averaged 20 s, and the learning criterion was three successive trials in a total time of less than 25 s. Training was carried out until this criterion was reached, to a maxi- mum of thirty trials.

After training on day 5, half the chicks were injected with 25 mg testosterone oenanthate in 0.1 ml sesame oil (Ts) and the other half with 0.1 ml sesame oil (Cs). Injections were intramuscular, 0.05 ml in each thigh. Testos- terone oenanthate is a long-acting androgen, being released over the 2 to 3 weeks after injection (Junkman 1952), and the dose used was identical to that used in the first studies of search behaviour (Rogers 1971; Andrew & Rogers 1972); this was later shown to be twice that which produced a maximal increase in copulation, attack and persistence in food searching (Andrew 1972b). Andrew (1972a, pp. 198 to 200) provides a discussion of the doses used in these studies in relation to adult physiological levels.

During the second week of life (days 8 to 11 inclusive), each chick received eleven trials a day: first, three control trials were given, and if the chick did not reach a criterion of a mean running time of 6 s or less, it was not tested further on that day; if it did run to criterion, it received three trials on which some characteristic of the runway had been changed, followed by two more control trials (same criterion as before) and finally three more trials on which another characteristic of the test environment had been changed. Details of the changes in test situation are summarized in Table I.

On each occasion, the time taken to reach the food dish and commence feeding was recorded (one or two isolated pecks were not regarded as commencing feeding). The chick was allowed 10 s feeding time on each trial and was removed from the runway after 60 s if it did not feed: on such occasions the time was recorded as 60 s.

Results Table II shows the time taken to run and

commence feeding (hereafter referred to as 'running times') before and after each change was introduced into the runway (the median of the mean of three trials for each chick). Results for the red food test are omitted from the table as no birds would take this food. Only one of the other types of change (the yellow panel at the end) produced no significant differences in

ARCHER: TESTOSTERONE AND DISTRACTABILITY 399

Table I. Changes Introduced into the Runway during Test Trials in Experiment 1

Day Trials* Runway change

8 4 - 6 Yellow polystyrene block placed be- neath food dish.

9-12 Red food replaces grey food. 9 4- 6 Yellow panel (30 x 11.3 cm) placed

on end wall of runway behind food dish. 9-12 Black and white panel (30 x 17-5 cm)

placed on end wall behind food dish. 10 4- 6 Two black and white panels placed half-

way along the runway, one on each side. 9-12 Walls of the feeding area white (in-

stead of the original blue) by inserting a white, three-sided piece of metal (each wall 30 x 20 cm) into the end of the runway.

11 4- 6 Blue food dish instead of transparent food dish.

9-12 Yellow food dish instead of transparent dish.

*Control trials (runway identical to that used during training) were 1 to 3 and 7 to 8.

running times for both Ts and Cs. All other changes significantly increased the times for the Cs, in the Ts there was no significant increase in running times for the black and white panel on the end wall or the yellow block under the food dish.

Table II. Experiment 1: Running Times (s) of

For changes no t directly connected with the food dish, the median running times showed a greater increase f rom control to experimental conditions for Cs and Ts, but only the black and white panels at the side produced a significant difference between T and C scores (Table II). On the other hand, the two changes at the food dish produced greater median increases in running times for the Ts than the Cs, a l though again the differences between Ts and Cs were not statistically significant (Table II).

Compar ison o f running times for the same birds when black and white panels were placed at the side and when the colour o f the food dish was changed revealed no significant differences for Ts (blue food dish: T = 12, N = 8, P > 0 - 1 ; yellow food dish: T = 16, N = 9, P > 0 . 1 ; Wilcoxon matched pairs test: Siegel 1956), but significant differences for Cs (blue food dish: T = 0, N - - 9, P < 0 . 0 1 , two-tailed; yellow food: T = 5, N = 9, P < 0 . 0 5 , two-tailed, Wilcoxon matched pairs test).

Discuss ion Two types o f change in the runway (black and

white panels on the end wall, yellow block under the food dish) significantly increased running times for Cs but not for Ts. Two further changes (black and white panels at the sides, white goal box) produced greater increases in running times for Cs than for Ts, but these differences

T and C Chicks After a Runway Change

Yellow Black and White Black and Yellow Yellow Blue food panel on white panel goal and white block under food dish end wall on end wall box at the side the food dish

dish

Median of mean control times for Ts w 3"7 5"0 4.0 4.2 4-7 3"8 3.8

Median of mean experimental times for Ts 4.0 10.0 9.0 11-8 7-0 12.8 7-8

Median difference for Ts 0.3 4-6 5"0t 7.7~: 3.0 9.1+ + 4.1, +

Median mean control times for Csw 5.3 4.5 3.6 3.7 6.3 3-0 3.3

Median of mean experimental times for Cs 4-3 23-3 26.8 44.0 12.7 8.0 4-3

Median differences for Cs 0.4 18"5" 21.0" 38.4~; 5"7t 5"0+ + 1 "2t

P value for comparison of median differences for Ts versus Cs (Mann-Whitney U-test, one-tailed) >0.1 >0.1 0.07 0.05 >0.1 >0-1 0.1

*P=0.01, tP=0.05,-0.02, :~P<0.01, for difference between control and experimental times (Wilcoxon matched- pairs tes0.

w times refer to trials immediately preceding each runway change (see Table I).


were only marginally significant (P=0.05 and P=0 .07 respectively). All four changes, together with another which did not significantly affect the running times for either Ts or Cs (yellow panel at the end), were concerned with aspects of the runway situation not involving the food dish itself, and can therefore be classed as 'irrelevant' to the ongoing response. Changes classed as 'relevant' to the ongoing response, i.e. involving the food dish (colour change to yellow or blue) produced a greater increase in median running times for Ts than Cs, although neither difference was statistically significant.

These results, although inconclusive for the food dish changes, are consistent with the predictions derived from Andrew's hypothesis (see introduction) that changes 'irrelevant' to the ongoing response would be more distracting for Cs than Ts but that changes relevant to the stimulus directing ongoing behaviour would be more distracting to Ts than Cs. One possible source of the relatively small differences between the Ts and the Cs when the colour of the dish was changed is the relative familiarity of the colours used: blue was the colour of the runway wails, and was therefore very familiar to the chicks, and yellow was the colour of the chicks themselves. Possibly, a more pronounced change in the characteristics of the food dish would produce a greater degree of distraction and separate the T and C chicks more. This was investigated in experiment two together with the effect of testosterone on chicks' reaction to changing the place of feeding.

Experiment 2 Introduction

Experiment 1 provided some evidence that 'irrelevant' changes were more distracting to C than T chicks but did not show any significant differences between the two conditions for changes directly related to the feeding response. In experiment 2, a similar procedure was used to the previous one, but only two types of novel stimuli were introduced into the runway, one being black and white panels on the side walls (which produced maximal differences between Ts and Cs in the first experiment) and the other being a black and white food dish. Thus the same pattern was used for both changes, and the food- dish change avoided the use of colours familiar to the chicks.

Several other methodological changes were made from experiment 1. First, the order of testing each chick in the two tests was such that

half the sample received one test on day 1 and half the sample received the other test. This controlled for the effects of previous testing, which were confounded in the design of experiment 1. Secondly, a larger sample of birds were used (N-----40) in order to detect differences between Ts and Cs despite the high degree of within-group variability which was observed in experiment 1. Thirdly, in view of a study of search behaviour in relation to different doses of testosterone (Andrew 1972b), which found that 12.5 mg produced maximal changes for copulation, attack and search behaviour in the young chick, this lower dose was used for experiment 2.

After administration of the two tests, each chick was tested on a third day using a runway with alcoves in the side walls halfway along, but otherwise exactly the same as the runway used previously. This test studied the effect of remov- ing the food dish from the end and substituting two identical dishes in the alcoves at the side. It was undertaken to provide information concerning a third prediction from Andrew's model, that search specifications with respect to a particular area of the environment are more per- sistent in Ts than Cs. This test, therefore, investigated whether Ts ran to an area previously containing the food dish when the dish had been moved to another place, and whether they were less able to switch to feeding in a different place than were Cs.

Methods The chicks (N = 40) were the same type as

those used in the first experiment, they were housed similarly during week 1 of life, and were trained in an identical runway on days 4, 5 and 6 of life: a different 'shaping' technique was used in that the start box was first placed near to the food dish at the end of the runway, and as the chick acquired the response it was gradually moved back down the runway, rather than the food dish being moved as in the previous experiment. Twenty training trials were given alto- gether, eight on day 4, and six on the other two days.

After training on day 6, the chicks were injected, half with testosterone oenanthate (12-5 mg, Ts) and half with sesame oil (Cs); the two conditions were matched as far as possible for runway performance.

During the second week of life (days 8 to 10 inclusive) each chick was given a series of test trials in the runway: on day 1 half the sample of


chicks (10 Ts and 10 Cs) received three control trials (criterion: mean running time of 6 s or less), and if they reached criterion this was followed by three trials on which two black and white panels (30 • 17.5 cm) were placed on the walls halfway along the runway, and finally by a further three control trials. (If a chick did not reach criterion on the control trials, it was not used further on that day). The remaining half of the sample (10 Ts and 10 Cs) received three control trials, three trials on which the (transparent) food dish was replaced by one painted in wide black and white stripes (similar to the side panels), and finally another three control trials. On the second day each bird received the treatment which it had not received on the previous day. On each occasion, the time taken to reach the food dish and commence feeding continuously for 6 s or more was recorded. This minimum time period was adopted because it was observed in experiment 1 that a change in the appearance of the food dish often led not to the delayed onset of feeding but to an inter- ruption of feeding after only a few pecks. Each chick was allowed 10 s feeding time, and was removed from the runway after 60 s if it did not feed.

On day 10, each chick received a further test session in a runway, identical to the one used on the other two days except for two alcoves (each 16.2 • 6.2 cm) in the side walls halfway along the runway. Each chick was first given three control trials (a pilot study had shown that the presence of the alcoves did not influence control running times) and if it reached criterion (as before) three further trials were given on which the food dish was absent from the custom- ary place at the end of the runway, but two identical dishes were present in the alcove. Again the chick was given 10 s feeding time, and was removed after 60 s if it had not fed in this time. Besides recording the time taken to commence feeding, the number of trials on which the chick went past the food dishes and the number on which it reached the end of the runway (where the food dish was originally placed) were recorded. The side on which the chick fed was also recorded, as was whether it changed sides during the 10 s feeding time. On this occasion a feeding response was recorded even if it had ceased feeding before 6 s, providing this represented a change between dishes, and not a complete cessation of feeding.

Results Table III shows the results for experiment 2.

For Ts and Cs, running times (defined as in experiment 1, see Results section) were significantly longer under both experimental conditions (changes at the side and at the dish) than during the corresponding control trials: this difference was, however, much greater for Cs than Ts when the change was at the side, and much greater for the Ts than for the Cs when the change was at the dish (see T values in Table III).

Comparisons of the mean increase in running times fi'om control to experimental trials for each chick revealed that when the change occurred at the dish, Ts showed significantly larger increases than Cs did whereas when the change occurred at the sides, Cs showed significantly larger increases than Ts did (Table III). Table III shows the very large difference in median values between Ts and Cs for the change at the sides: despite this large difference in the medians, the probability level for a comparison between Ts and Cs was relatively high (P=0.03), since there was considerable variability in the reaction of both Ts and Cs to the side panels: several chicks from each condition showed either little or no change in running times and others showed a maximal decrease (i.e. not reaching the end of the runway on any trial).

In the third test, involving changes in the place of feeding, both Ts and Cs showed similar running times, and there were no significant differences in the extent to which chicks from the two groups passed the food dishes on these trials, although more Ts than Cs did so. However, the number of changes of side during the three feeding trials (either between trials or within a trial) was significantly more for Ts than for the Cs, and the number of Ts changing sides was greater than the number of Cs doing so (Table III).

Discussion This experiment provided much clearer evid-

ence than the first one that a change involving the introduction of a particular 'irrelevant' stimulus affected the Cs to a greater extent than it did the Ts, but that the reverse was the case for a comparable change in the 'relevant' stimulus. This evidence provides stronger support for predictions 2 and 3 derived from Andrew's (1972a, b) hypothesis (see introduction to this paper), that Ts would be less able to accept changes in the stimulus characteristics


Table HI. Experiment 2: Running Times (s) of T and C Chicks Before and After Environmental Change

P value for Environmental change T C difference

N = 20 N = 19 between Ts and Cs

Black and white panel at sides

Black and white food dish

Dishes at the side

Median control times 4"0 3"8

Median experimental time 6.2 48.7

Median difference 2.0 42-7 0.03 t

P* <0.005 40.005 (T=19, N = 1 8 ) ( T = I , N = 19)

Median control time 4-3 4"0

Median experimental time 8.7 4"3

Median difference 5.2 1.3 0.015t

P* ,~0.005 0.01-0.005 ( T = 1, N = 19) ( T = 23.5, N = 17)

Median control time 3"0 3-0

Median experimental time 4"6 4.0

Median difference 1.5 0.7 > 0.1 t

P* 0.01-0.005 0.01-0.005 ( T = 29.5, N = 18) (T= 32, N = 18)

Median number of side 1 "0 0 0"01 t changes during feeding

Number of chicks changing 11 4 0" 1-0.05 sides

*Wilcoxon matched pairs test, one-tailed. ~Mann-Whitney U-test, one-tailed. ++Z 2 test, two-tailed.

relevant to their ongoing response but would show decreased distractibility by stimuli irrelevant to this response, than would Cs.

The results of the third test, involving changing the place of feeding, indicated that running speeds and visits to the previously reinforced area were not significantly greater in the Ts than the Cs, and thus did not support the prediction concerning increased persistence of responding to a feeding area. However, Ts did show significantly less consistency in their new feeding response than Cs did: Cs typically fed at the same side on each trial and did not break off to feed on the opposite side once they had commenced feeding within a trial. Thus although the Ts, like the Cs, were able to feed at the new location of the food dish, they showed more interrupted feeding and less consistency in their feeding place on successive trials once they had

started feeding there. Following Andrew's hypothesis, this could represent an indirect consequence of their previously-established 'persistence' of search specifications for a particular spatial locality, resulting in decreased ability to establish a new feeding area elsewhere. However, such an explanation is a post hoc one, since this was not among the predictions derived from Andrew's theory in the introduction.

General Discussion

In previous work, several experimental manipu- lations have been shown to affect distractability by newly-introduced irrelevant cues during a rewarded runway response. Thus, McFarland (1966) found that partially-reinforced doves were more distracted by a red flashing light than continuously-reinforced doves. Wickelgren & Isaacson (1963) found lesser increases in response


latencies by hippocampectomized than by sham-operated control rats when the floor of the runway was changed. Similarly, using auditory and visual distraction, Riddell, Roth- blat & Wilson (1969) found that the runway response of hippocampectomized rats was less affected than that of controls.

Several types of explanation have been offered for these and related results in terms of attention (McFarland 1966; Hendrickson, Kimble & Kimble 1969), response perseveration (Riddell et al., 1969), and fear (Antelman & Brown 1972), and the design of this type of runway experiment does not distinguish between the three possible explanations. In the present experiments, the direction of the difference in distractability between T and C chicks clearly depended on whether the introduced stimulus was irrelevant to the ongoing response (i.e. in the wails of the runway) or was relevant (at the dish). An effect on either the general level of fear or on response perseveration per se would have produced similar results irrespective of where the novel stimulus was introduced. This conclusion, together with other evidence reviewed briefly in the introduction (particularly data for visual scanning in a novel environment), strongly im- plies that attentional mechanisms are affected by testosterone. In this context, 'attention' refers to both effects on the position of the receptors and central changes determining which stimulus properties affect the ongoing response.

As indicated above, the results of the present experiments support two predictions derived from the theoretical model of Andrew (1972a): these were first that Ts would be less distracted from an ongoing response by changes in stimuli irrelevant to that response, and secondly that they would be more distracted when changes occurred in stimuli relevant to the ongoing response. The evidence was suggestive but more equivocal on a third prediction, concerning greater persistence in specifications for the place of feeding. All three changes can be explained according to Andrew's model as the consequence of a single primary change, increased stability of central specifications once these have become activated. Andrew (1972a) argued that the precise stimulus parameters represented in these central specifications would be unaffected by testosterone (rather, they would be a function of the particular test conditions used). Thus, only the stability of specifications would be increased by testosterone. The present results are all consistent with this model, but it may nevertheless

be fruitful to consider one further possible alternative which might account for the present findings.

This possibility is that testosterone directly affects mechanisms concerned with attention switching, so that Ts show a lesser tendency to switch attention from stimuli to which they are responding, whatever these happen to be. This possibility would account for the present findings with the changed panels at the sides of the runway and also for the more prolonged ex- amination of particular areas by Ts found in other studies (e.g. Andrew 1972a; Archer 1973). It would, however, not explain the greater distractability of Ts by changes in stimuli relevant to the ongoing response. Here, we should expect a general effect on attention switching to prolong attention to a stimulus being sought even if it were changed slightly in appearance (as was the food dish).

We can conclude, therefore, that Andrew's hypothesis of increased persistence of availability of search specifications remains the most adequate explanatory model for changes in runway behaviour produced by testosterone, and also for the findings in search tests and a novel environment, described in the introduction.

Acknowledgments This study was supported by a grant from the Medical Research Council of the United Kingdom to Professor R. J. Andrew. I thank Professor Andrew for his helpful comments throughout this work, and particularly for his comments on this paper.

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Antelman, S. M. & Brown, T. S. (1972). Hippocampal lesions and shuttle-box avoidance behavior: a fear hypothesis. Physiol. & Behav., 9, 15-20.

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natural levels of androgens in young and adult chickens. PhysioL & Behav.

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(Received 4 April 1973; revised 26 September 1973; M.S. number: 1221)

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