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The neural bases of haptic working memory

Amanda L. Kaas, M. Cornelia Stoeckel and Rainer Goebel


Introduction

When deciding which kiwi fruit or pear needs eating first or which drink has the right temperature to be consumed on a warm day, we are likely to explore and compare hardness or temperature using our hands. The process that enables us to keep the relevant information active for task performance over a short period of time is called ‘working memory’ (WM) [1]. WM allows us to hold stimulus characteristics on-line to guide behaviour in the absence of external cues or prompts [2]. Without active WM, initial percepts decay quickly with different time constants for different input modalities (Box 1).
The neural basis of haptic WM is usually studied indirectly in sequential discrimination paradigms, when information from one stimulus has to be retained for comparison with a second stimulus. In an attempt to avoid confounds due to hand and finger movements, passive stimulus presentation prevails over the more natural active exploration of tactile object features such as shape and texture. Haptic perception can be decomposed into tactile and kinaesthetic perception [3]. Functionally, the tactile (cutaneous) sense provides awareness of stimulation of the outer surface of the body, whereas the kinaesthetic sense provides us with an awareness of static and dynamic body posture. The term tactual perception was coined to refer to all perceptions mediated either by cutaneous sensibility and/or kinaesthesis. Haptic perception (and therefore haptic memory) is more than the sum of kinaesthetic and passive tactile processing. While passive tactile stimulation and isolated kinaesthesia produce tactual sensations, only active exploration allows for the perception of objects in space [4, 5]. Our review will include literature on tactual processing more generally, aiming to provide a fruitful basis for further investigations of haptic WM.
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