Modulación atencional en movimientos balísiticos y controlados

Abstract

The present doctoral thesis aimed at studying the interaction between attentional processes, motor responses and mental maps. In other words, the main goal of this work is to examine the relationship between motor control and attention. In the first chapter these two literatures are reviewed for the reader to be able to contextualized our object of study and the specific goals and predictions we had, which are specified in chapter 2. The series of experiments that were carried out in this dissertation are presented in three major chapters where the aforementioned relationship is analyzed at different levels. In chapter 3 we study the impact of the complexity of an initial motor action on the action itself, its influence on attentional effects such as Facilitation, Inhibition of return, and temporal preparation (i.e., foreperiod effect), as well as on rather motor effects such as the Simon effect. In chapter 4 we study the interrelation between attention and motor control by manipulating the degree of complexity of the motor action itself, i.e., its stimulus-response mapping, in order to see its impact on the size of the attentional effects (Facilitation, Inhibition of return and temporal preparation). Finally, in chapter 5, the motor control is analyzed on its most basic level, i.e., the mental representations, in order to learn more about the mental representation of different body parts in the brain. In chapter 3, entitled; Manipulation of the initial complexity of a reaching motor action, we study the interrelation between attention and the control of the initial movement. In the experimental task participants were asked to reach a bulls eye located one on each side of a computer screen. Participants were to reach one of the bulls eyes depending on the color of the target that was presented on the screen. The target was preceded by a peripheral non-predictive spatial cue in order to be able to measure spatial attentional orienting (Facilitation at the short cue-target SOA and Inhibition of return at the long SOA). Although location of the target was irrelevant (responses depended only on target color), the target was presented either to the left or to the right, in order to be able to measure the Simon effect. Our main interest was to study these attentional effects (Facilitation, IR, Simon, and the foreperiod or SOA effect) in order to see how they influence and are influenced by the initial complexity of the motor action. Three experiments were performed where we manipulated the difficulty of an initial motor action preceding the reaching action. In the first experiment, the subjects did not perform any action before the reaching action. In the second experiment, they had to press the z key and the m key on a computer keyboard with the index fingers of both hands. In the third experiment they started each trial by pressing an extended surface with both hand. The key difference between experiment 2 and experiment 3 consisted in the use in the initial action of the same (experiment 3) or different (experiment 2) muscles as those involved in the reaching movement. In other words; the key-press action of experiment 2 is performed with the extensor muscle of the fingers whereas the reaching action is performed with the deltoids muscles. Nevertheless the hand-press and reaching actions of experiment 3 are both performed with the deltoids muscles. Our hypothesis was that the latencies would be longer when the same muscle must perform two consecutive actions because the associated sequencing process is more complex. Furthermore, in order to study the progress of the effects in time and in muscular mechanics, we divided the overall reaction time (RT) of the reaching action (Contact Time) in several stages. On one hand, the time line consisted of Contact Time (CT; Time since the target¿s appearance until participants completed the motor action), which was divided in several time segment: Agonist premotor reaction time (APT; Time since the target,s appearance until the muscle starts to burn), Motor Reaction Time (MRT; Time since the agonist muscle starts to burn untill the arm starts to move) and Movement Time (MT; Time since the arm starts to move until the participant complete the action). On the other hand, we measured what we called the Intramuscular reaction time (IT; Time between the activations of the Agonist and the Antagonist muscles). The manipulation of the initial complexity leads to shorter latencies in the final action (CT) the simpler the preceding action. The slowest CT was observed in experiment 3 where the initial action was performed with the same muscles that the reaching action, thus involving the execution of sequential actions. This result has been previously reported in literature. In 1960 Henry and Rogers performed several studies, inspired by their memory drum theory, in which they examined the effect of movement complexity and its influence on reaction time. They concluded that more complex movements (i.e. motor actions involving various movements and various muscles) required more time in order for the action to be initiated and executed. This is because they involve a motor program which is more complicated in complex than in simpler movements. Even though our results in terms of CT are in line with this theory, in experiments 1 and 2 there were no differences neither in the initial action (APT) nor in the muscular process (IT). In fact, the action involved in experiment 2 is more complex because two sequential actions had to be performed as compared to experiment 1. In summary, there seem to be no significant difference in terms of action initiation between the conditions with one and two preceding movements (Franks, Nagelkerke y Van Donkelaar, 1998; Ketelaars, Garry y Franks, 1998). This is so despite the fact that the action complexity does affect the resulting CT. However, in experiment 3 the pre-motor reaction time is significantly longer in comparison with the experiments 1 and 2. This is in line with our hypothesis stating that the key-press movements does not interfere with the reaching action because different muscle groups are involved. In experiment 3, however, participants had to use the same muscles in both the reaching action and the preceding starting action. That is why the agonist pre-motor reaction time is longer in this condition than in experiment 2. This result leads to two conclusions. First, we have seen that the initial hands position may have an impact on the muscle latency. On the other hand, despite the fact that a sequential movement (experiment 2) leads to a longer CT in comparison with a simple movement (experiment 1), there are no differences in terms of action initiation (APT) between the two conditions. Therefore we can conclude that part of the motor action is programmed on-line while the movement is in progress. Another important goal of the present study was to examine the motor vs. pre-motor nature of attentional effects such as spatial attentional orienting (facilitation and IOR), temporal preparation (i.e., the SOA effect) and the Simon effect. The IOR effect was only detected in the action initiation stage (APT) but sometimes it was counteracted by facilitative sub-effects during the motor stages, despite the fact that IOR (i.e., slower RT to cued vs. uncued locations) was not present in any of these stages. Therefore the IOR effect, as observed in the final action (CT in our experiments and RT in other studies), seems to be in fact a compound of facilitative and inhibitive sub-effects, depending on the specific time stage (Howard, Lupiáñez & Tipper, 1999) or the processing component (Lupiáñez et al., 2007) which are analyzed. Since we have not found any relationship between the IOR and the Simon effect (which is considered a rather motor effect), it can be concluded that the nature of the IOR effect is mostly pre-motor (Chica & Lupiáñez, 2004; Howard, Lupiáñez & Tipper, 1999; Li y Lin, 2002a; Lupiáñez et al., 2001; Prime & Ward, 2004) The facilitation effect is present however during the motor stages, even though it appears mainly and more strongly during the pre-motor stages. Therefore we may conclude that the facilitation effect has a more pronounced motor component than the IOR effect. This is in line with several studies (Tipper, Rafal, Reuterlorenz et al., 1997; Tassinari, Aglioti, Chelazzi et al., 1994; Kathoon, Briand & Sereno, 2002; Mele, Savazzi, Marzi y Berlucchi, 2008; Posner & Cohen, 1984) suggesting that both mechanisms have rather different characteristics. The Simon effect is present in pre-motor stages of the movement (APT) in all the experiments, but also in the motor stages (MRT and MT) in experiment 3, which involves greater initial motor demands. Therefore we may conclude that the Simon effect affects stages subsequent to response selection and it can be observed during motor stages of the action, at least when the initial action complexity is increased. Hence our data from experiment 3 are not consistent with authors postulating a purely premotor nature for the Simon effect (Hommel, 1993a) Finally, the present research also sheds new light on several aspects of the SOA or Foreperiod effect. Our goal was to see whether this temporal orienting effect was present in the motor stages of the action in order to see whether temporal orienting mechanisms take place during the early stages of information processing, being independent from the motor programming or the action control in real time. We have observed that the effect of preparation in time also appears in the MRT when the complexity of the initial action is increased in experiment 2. This is so despite the fact that it arises during the pre-motor stages of movement (pre-motor agonist reaction time). Therefore we think that when the complexity of the initial action is increased, the influence of orienting mechanisms goes beyond the early perceptual processing stages, response selection and response preparation. This result is not totally new. Bjørklund (1992) found that the motor reaction time could be influenced by the SOA. When the complexity of the action further increased in experiment 3, there was an inversion of the temporal orienting effect, in the two motor stages that were analyzed. In other words, in MRT as well as in MT the main effect of SOA reversed, so that now participants were faster in the short SOA condition than in the long SOA condition. Therefore we can conclude that the difficulty of the initial action mainly influences the motor stages of the SOA effect. In addition, when this difficulty is raised there is an inversion of the SOA effect, most probably due to an increased need of control of the movement when the muscular activation is fast. In other words, it is possible that at the long SOA condition a greater control of response execution is necessary as a consequence of the early action initiation. The main goal of chapter 4 is to study the interrelation between attention and motor control, in particular the last stage of the motor program (v.gr., motor programming and movement execution). Our interest was to see how the complexity of the action, as indexed by the directness of the stimulus-response mapping, affected our attentional effects. More specifically, we wanted to analyze the impact of motor complexity (i.e., directness of the action) on the effect size of facilitation, IOR and foreperiod effects. In order to do so, we carried out two experiments, comparing the bull¿s eye reaching action (as described in chapter 3) with two different action of a greater complexity in movement programming and execution: an action consisting in reaching and pressing a small button, and the action of grasping a small cubicle and changing its position. We used the same temporal and muscular division used in chapter 3. We considered that the motor manipulation have an influence in the stimulus-response (S-R) mapping, so that simple movement (reaching bulls eye) has a more direct S-R mapping, and therefore bigger IOR effects were expected in this condition, according to Maylor (1985) and Pratt y Neggers (2008) results. We found that cueing effects (Facilitation and IR) were bigger when the motor complexity was lower or the movement was more direct, but only in premotor phases (APT). This is another evidence of the premotor nature of these effects. On the other hand, we can conclude that the reduction in facilitation is not the key to explain the beginning of IOR (Tipper et al., 1997), as greater IOR was observed in the condition producing also greater facilitation. One possible explanation is that the greater implication of prefrontal cortex in more controlled tasks such as those involving rather indirect S-R mapping entails tonic control of reflexive orienting structures (Khathoon et al., 2004). Therefore, the automatic effects of the signal (positive at the short SOA and negative at the long SOA) had a smaller size. Finally we found an inversion of the SOA effect in the motor phases (MRT and MT) as in the previous chapter, in special in high motor demand tasks, the inversion being greater the more motor demanding the task. Therefore, we can confirm that this inversion of the effect arouses because in the long SOA condition a greater control of response execution in necessary as a consequence of the early action initiation. In chapter 5 we point to other aspects of motor control beyond the movement itself (movement programming and execution), such as sensory-perceptual stages that take place before motor programming: mental maps that are used to represent sensory-motor information. In the previous chapter we found attentional differences when we manipulated the motor component of the movement. In the experiments described in chapter 5 we wish to know whether similar differences could be found in the different mental representations of the body parts. For this purpose we designed two experiments to study attentional differences between the two parts that conform the motor executor of our previous chapter; the whole fingers-hand. In order to study this dissociation we used an exogenous spatial orientation paradigm where participants had to detect a tactile stimulus that could appear on the back of their left hand or on the ring finger. The target was presented to one of the possible target locations (two locations in the finger and two locations in the hand) and preceded at either a short or a long stimulus-onset asynchronies (SOA) by a non predictive cue. The distribution of tappers in fingers and hand allowed us to make two different types of analyses. The intra-area analysis evaluated attentional effects in finger and hand separately. The inter-area analysis evaluated the same effects, i.e., facilitation and IOR, across the two adjacent areas, to see whether different effects are observed between and within areas. The results confirm the dissociation between these two areas. At the short SOA in the interarea analysis, where facilitation is expected, the data from both experiments clearly reveals an interaction between areas regarding the attentional effects that are observed. At the short SOA facilitation was in general observed only when the cue was presented in the hand. Thus, facilitation was observed at the hand (i.e., responses were faster when cue and target were presented in the hand, than when the cue was presented in the finger and the target in the hand), whereas IOR was observed in the finger (i.e., responses were faster when the cue was presented in the hand and the target was presented in the finger, than when both were presented in the finger). This process provides evidence about the main role of the hand in the activation of mental representations of fingers and hands, and at the same time support the hypothesis that fingers and hands have different mental representations. If they shared the same reference frame we should find the same pattern of cueing effects. In other words, the general facilitation observed when the cue is presented in the hand altered the normal cueing effect. Further evidence for different representations for fingers and hand came from the interareas IOR effect observed at the long SOA. The same way that IOR is reliably observed between hemifields (surely supporting a role of different hemifields representations, in different cerebral hemispheres) (Weger, Al-Aidroos & Pratt, 2008) IOR was observed between finger and hand in our two experiments, thus supporting that they are represented as different areas. In this vein, Haggard (2005) showed that the hands are allocentrically represented, whereas fingers are coded somatotopically. Similarly, the studies about finger agnosia (Benton, 1959; Gerstmann, 1942, Mayer, Martory et al., 1999; Kinsbourne & Warrington, 1962; Anema, Wokswijk, Ruis and Dijkerman, 2008) conclude that fingers could have separate representations from the hand. Finally, in Chapter 6 a general discussion of the results is presented, in the context of the discussion about the relationship between attention and motor control that is the main theme of our thesis. Also, some general conclusions are extracted, which are also provided in English.