Estadístico de la prueba

I t is ccmmon knowledge th a t c o n d itio n e d suppression can d e c lin e w ith repeated CS-ÜS p a irin g s (eg. Church, Raymond and Beauchamp,1967). One e xp la n a tio n f o r t h is is th a t the p a in fu ln e s s o f the shocks d e c lin e s w ith repeated p re s e n ta tio n . That is , shock p re s e n ta tio n , per se, is re s p o n s ib le f o r some o f th e US pre-exposure e ffe c t; C apaldi, C h e ffe r, V iv e iro s , Davidson and Campbell (1985) have argued s tro n g ly f o r t h is . T his n o n -a s s o c ia tiv e e xp la n a tio n is n o t covered by any o f th e th e o rie s I have discussed.

Events th a t precede Ih e US

A commonly o ffe re d e x p la n a tio n f o r the US pre-exposure e ffe c t is th a t a context-U S a s s o c ia tio n is formed d u rin g pre-exposure, and th is a s s o c ia tio n re ta rd s le a rn in g o f a subsequent CS-US a s s o c ia tio n , because o f b lo c k in g , a s s o c ia tiv e in te rfe re n c e , o r some o th e r mechanism. I f t h is is so, we would expect a change o f c o n te xt to a tte n u a te th e US pre-exposure e ffe c t. C onfirm ing e x p e c ta tio n s , th is has been found w ith autoshaping in doves (Balsam and Schwartz, 1981), and w ith c o n d itio n e d suppression in ra ts (Baker, M e rcie r, Gabel and Baker, 1981). Dweck and Wagner (1970) w ith l i c k suppression in r a ts , and Tomie (1976) w ith autoshaping in pigeons, have shown th a t sim ple exposure to the c o n te xt g re a tly reduces the e ffe c t o f US pre-exposures. Thus i t seems h ig h ly l i k e l y th a t th e re is a context-U S a s s o c ia tio n , and t h is can b lo ck c o n d itio n in g to the nom inal CS. To lend fu r th e r support to th is id e a , Tomie (1976) gave US pre-exposures w h ile a tone was presented f o r the whole session (th u s , the tone was a background o r c o n te x tu a l cue), and showed th a t h is tone could b lo ck CS— >US c o n d itio n in g when used as a more co n ve n tio n a l d is c re te s tim u lu s .

However, Baker f i t aJL (1981, Experiment 2) re p o rt data w hich suggest th a t US o n ly t r i a l s produce the US pre-exposure e ffe c t n o t o n ly by a context-U S a s s o c ia tio n b lo c k in g subsequent c o n d itio n in g , but a lso by the US o n ly t r i a l s a ffe c tin g the US's p r e d ic ta b ilit y . T h e ir experim ent used co n d itio n e d suppression o f le v e r p re ssin g . A ll fo u r groups o f r a ts were te s te d by p a irin g a c lic k e r w ith shock. The groups d iffe re d in t h e ir p revio us tre a tm e n t; Group SH had unpaired shock pre-exposure; Group OB (o th e r box) a ls o had unpaired shock

pre-e3q>osure b u t in a d iffe r e n t c o n te x t; Group L had the pre-exposed shocks s ig n a lle d by a lig h t CS; and Group C had no s tim u li presented. On the b ase line recovery days a fte r t h is pre-exposure, Group SH, and to a le s s e r e x te n t Group L , showed fe a r to the co n te xt by m a in ta in in g a reduced ba se lin e response r a te ; ie , a context-sh ock a s s o c ia tio n . On te s t. Group SH d isp la ye d very much le s s suppression than Group C, dem onstrating the usual US pre-exposure e ffe c t; and Group OB suppressed m a rg in a lly more than Group SH, so th a t in th is experim ent a change o f co n te xt o n ly s lig h t ly reduced the US pre-exposure e ffe c t. The r e s u lt o f in te r e s t is th a t Group L 's suppression was s im ila r to Group C. So, even though Group L was more a fra id o f the context than Group OB, th e data suggest i t s t i l l le a rn t th e c lic k e r — >shock a s s o c ia tio n fa s te r than Group OB. This cannot be explained by the c o n te xt b lo c k in g account. One p o s s ib ility is th a t th e u n p re d icta b le nature o f the US p re se n ta tio n s leads to re ta rd e d le a rn in g ( ie , the a s s o c ia b ility o f th e US decreases). In Group OB, th e ra ts le a rn th a t shocks are u n p re d ic ta b le , and so are slow er to le a rn th a t the shocks are preceded by c lic k e r p re s e n ta tio n s .