Z . Tierpsychol., 50, 201-202 (1979) @ 1979 Verlag Paul Parey, Berlin und Hamburg lSSN 0044-3573 I ASTM-Coden: ZETIAG

Kommentar / Commentary

Arbeitsgvuppe fur Verhaltensforschung, Abteilung fur Biologie, Ruhr-Uniuersitiit Bochum

“Functional Validation” - a Necessary Concept?

By E. CURIO

In an important paper in this journal RUSSOCK and HALE (1979) reported upon a little-studied effect external stimuli can have for the maintenance of a behaviour pattern in ontogeny. Here I take u p the issue of whether the phenomenon described deserves a name of its own o r whether older concepts might apply. 1 wish t o stress the convention that a new label should be invented only if the phenomenon which it is proposed t o designate differs in a t least one aspect from older concepts relating to other (similar) phenomena. Even then the concepts may prove to be “injunctive”, i.e. connected by a whole series of intergrading phenomena (HASSENSTEIN 1955).

RUSSOCK and HALE (1979) found that incubator-hatched domestic chicks behave toward the taped maternal food call by approachingiattending the sound source. The behaviour is qualitatively much the same as that shown to a broody hen calling and simultaneously tid- bitting the first time after exodus from the nest. Responsiveness of artificially reared chicks to the food call virtually disappears after the third day. However, an exposure of only 7.5 niin in the last 12 h before the third day maintains responsiveness a t five days of age, i.e. the behaviour is said to be “functionally validated” so as still to appear a t a time when without that exposure it would have regressed. For reasons of terminological parsimony, one could ask to what extent “functional validation” of the chick’s responsiveness differs from “priming”.

The authors think HINDE’S (1970, p.509) definition of “priming” does not apply to their finding. HINDE stares: “In these (cases) elicitation of the response facilitates its sub- sequent elicitation by stimulus situations which appear to share no characteristic with that which first elicited it.” If this definition holds, priming indeed differs substantially from “functional validation” as described for the chicks, and hence a distinction between the two would be fully justified. Unfortunately, HINDE’S definition contrasts with his account of NOIROT’S well-known work with laboratory mice. This work demonstrates that it is not the elicitation of a response that facilitates its subsequent elicitation. I t is rather the exposure t o an appropriate stimulus, as in the chicks’ case, that leads t o this effect: The exposure to a live one-day-old baby mouse increases responsiveness to retrieve a drowned baby that nor- mally would not elicit the retrieving response. Increase of responsiveness is not even con- tingent on prior performance of the response: If a live baby mouse has been placed in her nest, an inexperienced 9 will retrieve a dead baby, without having had experience with the retrieval response itself. Hence, mere exposure to an appropriate stimulus led to facilitation of a response, thus nullifying the distinction between priming and “functional validation” in one respect.

Furthermore, a live and a drowned baby mouse share a host of potentially relevam btimulus characteristics. Even if tactile cues are shielded off the facilitatory effect remains (HIND, 1970, p.308). But clearly the two stimuli may still share olfactory cues. Hence, stimulus sharing cannot be ruled out in the examples given by HINDE as conforming to his definition. The degree of stimulus specificity necessary for facilitation to occur has so far been studied neither in the chicks of RUSSOCK and HALE nor in any study of priming. SHALTER (1978) found that pied flycatchers (Ficedula hypoleuca) are induced to mob a stuffed pigmy

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202 CURIO, “Functional Validation” - a Necessary Concept?

owl (Glaucidiurn passerinurn) by mobbing a live pigmy owl. Mobbing a human d id not have this facilitatory effect. Hence, some degree of stimulus specificity may well prove necessary for priming to operate, but much more work is needed here, as also in other possible cases of priming (e. g., EIBL-EIBESFELDT 1958).

To escape the dilemma one could redefine priming to f i t the evidence in mice and chicks; one would have to allow for mere exposure being effective and for similarity (if not identity) of the priming and the test stimulus. Or , one could leave as it is HINDE’S definition of a behaviour category (with possibly no correlate ir. the real world) and coin a new term covering the observations in mice and chicks. Here I ropose to call both phenomena priming, because it is the older term, and redefine it accordingfy.

There remain two featurec which, as kindly pointed out by Dr. RUSSOCK (in litt.) to the editors of 2. Tierpsychol., might still distinguish the chick findings from priming as illustrated by NOIROT’S work.

1. There is no indication that priming is restricted to a sensitive period (at times more carefully called “responsive period”) as is inferred for “functional validation” by RUSSOCK and HALE. However, the evidence for a scnsitive period is a t best suggestive; n o control group of chicks was firsr exposed to the food call a t a n age when responsiveness to it had regressed. This additional experiment could easily have shown whether a later test would have failed to elicit the appropriate response to the sound. Such failure would have supported the claim of a sensitive period. Even so, a possible sensitive period remains unexamined in the other cases cited (mice, pied flycatcher), and thus could not immediately serve as a distinguishing character.

2 . There remains the fact that the chicks’ response is maintained beyond an age a t which, without exposure to the food call, it would have disappeared. Since it is not known whether stirnuIi from babies serv: to maintain marernal behaviour in female mice in the long rerm, the distinction between the observations in mice and chicks cannot a t present be upheld.

Priming and “functional validation” are a t least similar processes i f reference is made to fact, not to an inappropriate definition. Further work has to show whether the t w o criteria pointed out by Dr. RUSSOCK (sensitive period; maintenance) will serve as a useful distinction or will make the two concepts collapse into one.

In conclusion:

Literature cited

EIBL-EIBBSFELDT, I. VON (1958): Putoritrs putorius (L.). Beutefang I (Toten von Wander-

HASSENSTEIN, B. (1955): Abbildende Begriffe. 2001. Anz. Suppl. 18, 197-202 HINDE,

RUSSOCK, H . I., and E. B. HALE (1979): Functional validation of the Gallus chick’s

SHALTER, M. D. (1978): Mobbing in the pied flycatcher. Effect of experiencing a live

ratten). Inst. Wiss. Film, Gottingen.

R. A, (1970): Animal Behaviour. 2nd ed. McGraw-Hill, New York, pp.308,509.

response to the maternal food call. 2. Tierpsychol. 49, 250-259.

owl on responses to a stuffed facsimile. Z. Tierpsychol. 47, 173-179.

Author’s address: E. CURIO, Arbeitsgruppe f. Verhaltensforschung, Abt. f. Biologie, Postfach 10 21 48, D-4630 Bochum 1.