On aims and methods in the neuroimaging of derived relations

Abstract

Ingenious and seemingly powerful technologies have been developed recently that enable the visualization in some detail of events in the brain concomitant upon the ongoing behavioral performance of a human participant. Measurement of such brain events offers at the very least a new set of dependent variables in relation to which the independent variables familiarly manipulated in the operant laboratory may be explored. Two related paradigms in which a start has been made in such research concern the derivation of novel or emergent relations from a baseline set of trained relations, and include the phenomenon of transitive inference (TI), observed in studies of stimulus equivalence (SE) and serial learning (SL) or seriation. This paper reviews some published and forthcoming neuroimaging studies of these and related phenomena, and considers how this line of research both demands and represents a welcome synthesis between types of question and levels of explanation in behavioral science that often have been seen as antithetical.

Figure 1. Top: Serial position effect in serial learning.

Latencies of trained responses at the end of training in serial learning as a function of the position of the stimuli on the implicit series in an instructed versus an uninstructed group of participants. Bottom: Symbolic distance effect in serial learning. Latencies of transitive responses after serial learning as a function of number of intervening stimuli in an instructed versus an uninstructed group of participants. (Modified from Anderson & Dickins, 2003).

Figure 2. Timelines for arbitrary MTS compared with identity matching with zero and nonzero delays (D. W. Dickins, 2003) (not drawn to any particular scale).

Upper lines: onset and offset of sample stimulus (open) and comparison stimuli (hatched), with or without an interstimulus interval (nonzero or zero delay). Response latency is measured from the onset of the comparison stimuli until the response. Lower boxes: postulated succession of hypothetical component processes. Key: 1  =  registration, 2  =  retrieval of trained relation, 3  =  scan of comparisons, 4  =  recognition of correct comparison, 5  =  organisation of response; black unnumbered box indicates no postulated process occurring. See text for explanation.

Figure 3. Effects of delay on identity matching and arbitrary (i.e., symbolic) MTS tasks.

Shown are the mean of the median response latencies after zero and nonzero delays between sample offset and onset of the six comparison stimuli.

Figure 4. Schematic representation of shared and specific features of the three types of matching-to-sample tasks employed in D. W. Dickins et al. (2001).

The results of this fMRI investigation conformed more closely with (b). (a) An additive hierarchy in which the upper tasks encompass all of the features of those below them, plus specific features of their own. (b) A Venn diagram in which each task shares some features with one and some with both of the other tasks, but also has its own peculiar features.

Figure 5. Glass brains showing significant differences when activations obtained on various control and experimental tasks were compared (Dickins et al., 2002.

On the right of each pair is a transverse section, and on the left is a saggital view of a transparent brain, with the anterior pole to the right. Dark areas indicate significant clusters of voxels, and the salient ones are labelled with their Brodmann areas. (a) full identity matching task minus asterisk control task; (b) trained relations task minus full identity task; (c) full identity task minus trained relations task; and (d) trained relations task minus asterisk control task.