No effect of hippocampal lesions on stimulus-response bindings

- Hippocampus is thought important for rapid binding of stimuli (S) and responses (R).
- Six patients with hippocampal damage showed evidence of normal S-R bindings.
- Both patients and controls showed priming of object size judgments.
- Patients and controls showed equivalent priming reductions when responses reversed.
- The hippocampus is not necessary for this type of S-R binding.

The hippocampus is believed to be important for rapid learning of arbitrary stimulus-response contingencies, or S-R bindings. In support of this, Schnyer et al. (2006) (Experiment 2) measured priming of reaction times (RTs) to categorise visual objects, and found that patients with medial temporal lobe damage, unlike healthy controls, failed to show evidence of reduced priming when response contingencies were reversed between initial and repeated categorisation of objects (a signature of S-R bindings). We ran a similar though extended object classification task on 6 patients who appear to have selective hippocampal lesions, together with 24 age-matched controls. Unlike Schnyer et al. (2006), we found that reversing response contingencies abolished priming in both controls and patients. Bayes Factors provided no reason to believe that response reversal had less effect on patients than controls. We therefore conclude that it is unlikely that the hippocampus is needed for S-R bindings.