Fig. 3.

‘Amodal’ versus ‘true’ interactions between sensory modalities. Processing of different sensory modalities may interact ‘truly’, that is, in a stimulus-specific manner, or the interaction may be ‘amodal’, that is, between the ‘values’ elicited by the respective stimuli rather than the actual stimulus features. a Odour-shock learning exemplifies an ‘amodal’ interaction: Shock and probably all other aversive stimuli feed into a common ‘Bad!’ signal, which interacts with the particular stimulus features of the odour. That is, the odour is associated with ‘something Bad!’ and thus will subsequently be avoided. b Sensory pre-conditioning on the other hand requires a ‘true’ interaction between sensory modalities: Initially, an odour and a visual cue are presented simultaneously in the absence of any reinforcer. This joint presentation endows both stimuli with the ability to ‘call up’ each other in a stimulus-specific manner. When in a subsequent experimental phase, one of the two is paired with aversive heat, the other is ‘called up’ as well and is also associated with the ‘Bad!’ signal. c Such stimulus-specific interaction is also required for biconditional discrimination, that is, learning about the combinations of odours and visual cues: Representations of both the odour and the visual cue must converge to form an additional joint representation of the two. This joint representation then can be associated with the ‘Bad!’ signal