Glover’s proposal that planning and execution control of actions are two separate processes which follow two separate and inde

Commentary on GLOVER

Abstract: 79 words

Main text: 583 words

References: 209 words

Total text: 954 Words

AT LEAST SOME ELECTROPHYSIOLOGICAL AND BEHAVIOURAL DATA CANNOT BE RECONCILED WITH THE PLANNING/CONTROL MODEL

P. Paolo Battaglini

BRAIN Center for Neuroscience

Università di Trieste,

via Fleming 22,

34127 Trieste,

Italy

+39 040 5587183

battagli@univ.trieste.it

Paolo Bernardis

Dipartimento di Psicologia and BRAIN Center for Neuroscience

Università di Trieste,

via S. Anastasio 12

34143 Trieste

Italy

+39 040 5582732

bernardis@psicoserver.univ.trieste.it

Nicola Bruno

Dipartimento di Psicologia and BRAIN Center for Neuroscience

Università di Trieste,

via S. Anastasio 12

34143 Trieste

Italy

+39 040 55827451

nicola.bruno@univ.trieste.it

Abstract.

The planning/control distinction is an important tool in the study of sensorymotor transformations. However, published data from our laboratories suggest that, contrary to what predicted by the proposed model, (i) structures in the superior parietal lobe of both monkeys and humans can be involved in movement planning; and (ii) fast pointing actions can be immune to visual illusions even if they are performed without visual feedback. The planning/control model as proposed by Glover is almost certainly too schematic.

Can we make a sharp distinction between planning and control in human action production? There is little doubt that planning must precede the onset of movement, whereas online control must become increasingly important as the action progresses. It remains to be seen, however, whether this obvious temporal ordering is also implemented in separate neural structures running on the basis of different internal representations. Although Glover's model is remarkably successful in accounting for a large body of data, it seems to us that other results remain problematic in the light of a sharp planning/control distinction.

One of us (Battaglini) has described arm-movement related neurons in area V6A of the macaque superior parietal lobe. Comparing neural activity with arm electromyographic recordings clearly showed that several of these neurons discharged prior to the onset of movement (Galletti, Fattori, Kutz & Battaglini, 1997). Further analyses suggested that as many as 30% of these V6A neurons may be activated before the onset of a reaching movement (Fattori, Gamberini, Kutz, & Galletti, 2001). In a lesion study, small bilateral lesions in the same area V6A of the green monkey produced deficits in fast, balistic reaching and grasping. When presented with food (raisins) at specific egocentric distances, in initial trials lesioned monkeys misreached the targets several times and only in later trials they reached correctly from start. Morevoer, lesioned monkeys failed to generalize their training to other egocentric distances, as one would expect if they suffered from a planning deficit. Thus, contrary to Glover's predictions for humans, these data suggest that the monkey SPL may be involved in both planning and control. Although these results may reflect functional differences between the human and monkey brain structures (but see Galletti, Battaglini, & Fattori, 1997), in EEG studies of reaching in humans Battaglini also found a clear activation at the SPL before the onset of movement (Battaglini , Naranjo, & Brovelli, 2002). These findings suggest that Glover's identification of the human SPL as the site of online control may be too schematic.

Similarly, human studies from the second of our laboratories (Bruno) may be interpreted as evidence that Glover's conception of the internal representations used by planning and control is also too schematic. In a study of bimanual, fast reaching to the endpoints of a surface subjected to Kanizsa's compression illusion (Bruno & Bernardis, 2002), Bruno measured performance in two motor conditions. In the first of these conditions, blindfolded actors extended their arms until their hands where in the position where they had seen the endpoint of the surface. Results showed no hints of compression, although visual discrimination data showed the usual 5% compression reported in previous studies (Kanizsa, 1975). Given that these actions were performed quickly and without visual feedback, in the planning/control framework they should have reflected a greater influence of the "cognitive" representations used for planning. However, the results failed to show the "cognitive" effect of the illusion. Even more convincingly, in a second condition actors simply placed their hand in front of their chest, in spatial alignment with the surface endopoint, without extending their arms completely. Given that this second action corresponded to the early part of bimanual reaching, in the planning/control framework it should have reflected an even greater influence of the "cognitive" representation. However, again the results failed to show any cognitive effect. In fact, there was no difference with the full reaching condition. Comparable results were found in a pointing study, which also generalized them to a variant of Müller-Lyer's illusion (Bruno & Bernardis, 2003).

References

Battaglini, P. P., Muzur, A.., & Skrap, M. (2003). Visuomotor deficits and fast recovery after area V6A lesion in monkeys. Behavioural Brain Research, 139, 115-122.

Battaglini, P. P., Muzur, A.., Galletti, C., Skrap, M., Brovelli, A.. & Fattori, P. (2002). Experimental Brain Research, 144, 419-422.

Bruno, N., & Bernardis, P. (2002). Dissociating perception and action in Kanizsa’s compression illusion. Psychonomic Bulletin & Review, 9, 723-730.

Battaglini , P.P., Naranjo, J.R., & Brovelli, A.. (2002) EEG study of the fronto-parietal cortical network during reaching movements. FENS Abstr, vol. 1, 070.1.

Bruno, N., & Bernardis, P. (2003). When does action resist visual illusions? Effector position modulates illusory influences on motor responses. Experimental Brain Research, in press.

Fattori, P., Gamberini, M., Kutz, D. F., & Galletti, C. (2001). Arm-reaching neurons in the parietal area V6A of the macaque monkey. European Journal of Neuroscience, 13, 2309-2313.

Galletti, C., Fattori, P., Kutz, D. F., & Battaglini, P. P. (1997). Arm-movement related neurons in the visual area V6A of the macaque superior parietal lobule. European Journal of Neuroscience, 9, 410-413.

Galletti, C., Battaglini, P. P., Fattori, P. (1997). The posterior parietal cortex in humans and monkeys. News in Physiological Sciences, 12, 166-171.

Kanizsa, G.(1975) Amodal completion and phenomenal shrinkage of surfaces in the visual field.