Unconscious semantic priming from pictures Roberto Dell'Acqua * , Jonathan Grainger CREPCO±CNRS, Universite  de Provence, Provence, France Received 18 May 1999; received in revised form 25 May 1999; accepted 23 July 1999 Abstract Three experiments examined the effects of unconsciously presented picture primes on semantic categorization and naming responses to both word and picture targets. Picture naming and word categorization responses to targets were faster and more accurate when the picture primes belonged to the same semantic category as the targets, so called priming effect. No priming was found when subjects performed a word reading task. When priming was evident, no difference was found between responses to targets that were nominally identical to primes (e.g. the picture of a lion followed by either the word LION or the picture of a lion) compared with nominally different targets from the same semantic category as the primes (e.g. the picture of an ELEPHANT followed by either the word LION or the picture of a lion). Responding did not differ signi®cantly from chance when subjects were asked to categorize the primes as natural objects vs. artifacts or as meaningful vs. meaningless objects in three distinct forced- choice unspeeded tasks. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Priming; Unconscious cognition 1. Introduction Can semantic information be extracted from unconsciously presented stimuli and subsequently in¯uence overt behavior? This question has attracted attention from scientists for well over a century and the debate continues to rage to this day (e.g. Draine & Greenwald, 1998). The reason why no clear cut answer has yet been provided, is mainly because the question hides two dif®cult methodological problems. What is the appropriate operational de®nition of the term unconscious? What is the appropriate measure of the in¯uence of semantic information on overt behavior? Concerning the ®rst question, the problem is that too conservative a de®ni- Cognition 73 (1999) B1±B15 COGNITION 0010-0277/99/$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S0010-0277(99)00049-9 www.elsevier.com/locate/cognit * Corresponding author. Dipartimenti di Psicologia, 8 Via Venezia, 35100 Padova, Italy. Tel.: 1 39- 049-827-6545; fax: 1 39-049-827-6511. E-mail address: dellacqu@psy.unipd.it (R. Dell'Acqua)