Exp Brain Res (2008) 190:493–498 DOI 10.1007/s00221-008-1538-y 123 RESEARCH NOTE Grasp cueing and joint attention Nadja Tschentscher · Martin H. Fischer Received: 20 March 2008 / Accepted: 4 August 2008 / Published online: 20 August 2008 © Springer-Verlag 2008 Abstract We studied how two diVerent hand posture cues aVect joint attention in normal observers. Visual targets appeared over lateralized objects, with diVerent delays after centrally presented hand postures. Attention was cued by either hand direction or the congruency between hand aper- ture and object size. Participants pressed a button when they detected a target. Direction cues alone facilitated target detection following short delays but aperture cues alone were ineVective. In contrast, when hand postures combined direction and aperture cues, aperture congruency eVects without directional congruency eVects emerged and per- sisted, but only for power grips. These results suggest that parallel parameter speciWcation makes joint attention mech- anisms exquisitely sensitive to the timing and content of contextual cues. Keywords Grasping · Joint attention · Imitation · Mirror neurons Introduction Joint attention describes changes in one’s visuo-motor potential after observing somebody else’s directional behavior. This ability to infer and attend to the target of another person’s actions before the action is completed emerges soon after birth (e.g., Hood et al. 1998) and then leads to overt changes of behavior, such as directing one’s own gaze or body towards that same target. In older chil- dren and adults, similar directional responses can also be covert, e.g., an increased visual sensitivity without changes in behavior. Such covert joint attention can be measured with behavioral or neuroscientiWc methods, and in all sen- sory modalities (e.g., Posner 2004). A popular approach compares detection speed for visual targets in congruent and incongruent trials. In congruent tri- als targets appear on the side that was cued by a directional or deictic signal; in incongruent trials they appear on the opposite side. Congruent trials improve performance com- pared to incongruent trials, and several studies with gaze, head, or body cues have revealed a specialized and auto- matic joint attention mechanism that rapidly extracts inten- tion-related directional information. This mechanism may be implemented either as an inhibitory neuronal hierarchy in the superior temporal sulcus (e.g., Perrett and Emery 1994), or within the human mirror neuron system (MNS) which utilizes neurons that code for both the perception and execution of similar actions (e.g., Rizzolatti and Craighero 2004). The ideo-motor theory (James 1890) already sug- gested that viewing someone else performing a movement results in activation of that movement pattern in the observer. More recent research (e.g., Jansson et al. 2007) supports this proposed relationship between the representa- tion of an action and the resulting movement: movements are activated through “images” of an action’s eVect that consists of sensory feedback produced by the observer’s similar actions before. Thus, observation of another per- son’s actions results in pre-activation of a similar motor representation in the observer, which can then help to imi- tate the observed behavior. Ideo-motor theory has recently received considerable empirical support. For example, transcranial magnetic N. Tschentscher · M. H. Fischer (&) School of Psychology, University of Dundee, Dundee DD1 4HN, Scotland, UK e-mail: m.h.Wscher@dundee.ac.uk N. Tschentscher Psychology Department, University of Münster, Münster, Germany