Selective attention in linked , minimally cognitive agents

We investigate minimally cognitive agents for attention and control of action. VA (visual agent) can attend to one target while ignoring another, and then reallocate processing. Here we review some of our previous results with VA, showing how an analysis of a minimally cognitive agent can both support previous ideas of selective attention and action, as well as suggest new possibilities. We investigate a simple case in which multiple agents are combined to solve tasks that no single agent can complete on its own. Minimally cognitive 3 Cognitive agents and their environment interact within a continuous perception-action cycle: perceptions guide actions, actions alter the environment, and the altered environment in turn generates new perceptions (Gibson, 1979). However, computational models in psychology have tended not to focus on the dynamic nature of the perception-action loop. Even models of perception-action linkage are usually static in nature: processing begins with the presentation of static stimuli, and ends with the selection of an action which has no effect on the stimulus environment (Cohen, Dunbar, & McClelland, 1990; Schneider, 1995; Ward, 1999). In many cases, action is not modelled seriously, perhaps consisting of an activated output node representing one of several discrete alternative responses. In this respect, the models largely follow the available empirical work. Although much is known about the capacity, time-course, and brain regions important for selective attention and action, in the large majority of studies, the responses measured have little to do with the dynamic nature of the perception-action cycle. Usually, participants make some discrete response, like a keypress, and the trial ends with no impact on the agent’s environment. Theories and models generated for static situations and discrete responses may be inadequate for more interesting tasks and realistic agent-environment interaction. We want to push psychological models towards more complex forms of action, and to encourage thinking about how selective attention and action work within the perception-action cycle. In this respect, a useful class of models, sometimes called embodied, situated, and dynamical (ESD) agents, stress what Clark (1999) calls “the unexpected intimacy between the brain, body, and world”. The ESD approach emphasizes the contextually-bound nature of solutions to cognitive problems, and therefore considers specific tasks in their entirety, rather than isolated but general-purpose attention, perception, or motor subsystems. In ESD agents, control of action does not arise through general-purpose representation, but emerges from a Minimally cognitive 4 distributed system involving the brain, body, and world. An important form of the ESD approach for our purposes is the “minimally cognitive” agent, developed by Beer (1996). “Minimally cognitive” agents are intended to be tractable models that are embodied, situated, dynamic, and that can do interesting cognitive tasks. For example, Figure 1 shows the visual agent (VA) developed by Slocum et al (2000), evolved by genetic algorithm to selectively attend and respond to targets in its 2D environment. The agent was equipped with an array of proximity sensors, left and right motor units to control its movement, and a small hidden layer of eight units. The targets “fell” from the top of the 2D environment, and VA was meant to “catch” them by moving under them before impact. In our simulations, the two targets fell straight down, and with constant velocity, the first target (T1) by definition having greater velocity than the second target (T2). Following Slocum et al (2000), the agent was controlled by a continuous-time recurrent neural network (CTRNN), with a reasonably generic network architecture (see Figure 1). Although catching one target is trivial, catching two targets is definitely not. Catching two targets requires numerous cognitive operations for success, including: (1) correctly prioritizing one of the two targets for immediate action; (2) before impact, tieing motor systems to the movements of the selected target, and insulating them from the effects of the other target; and (3) after catching the first target, the second target, which was previously insulated from the motor system, must now be allowed to control the motor system. These processes of selection, response control, and reconfiguration following a change of targets are all important themes in current selective attention research (for an overview, see Driver, 2001). Not only does the task require interesting cognitive abilities, but it is also a good example of an embodied agent, embedded within a genuine perception-action loop: action involves an extended sequence of motor commands in response to sensory inputs: the senses Minimally cognitive 5 guide action, and action generates new sensory inputs. VA therefore seems like a useful starting place for looking at a new class of models, that extend beyond the limits of static situations, free of any meaningful agent-environment interaction. We have then recently undertaken psychological analyses of this agent. Our aim was to understand the bases for selective attention and control of action within the agent. Our approach might be fairly described as “artificial comparative psychology”. We are seeking to understand the psychological principles that allow VA to control its attention, and then compare to what is found in the human attention literature. We reasoned that, as long as VA is doing a genuine selective attention task, two outcomes are possible, and both are interesting. First, it might be that VA operates according to new principles not yet seen in the human literature. In this case, VA acts as a model to new experimentation and theory. Second, it might be that the agent operates according to models already developed in the human literature. In this case, VA serves as a tractable, embodied model system. However, the validity of either outcome depends upon the validity of the selective attention, an issue we address in greater detail elsewhere (Ward & Ward, in press). The psychology of attention in a minimally cognitive agent In fact, our analyses of VA uncovered both established and novel concepts in the human attention literature. Here we briefly review our analyses of VA, describing its psychological mechanisms for attention and control; however, complete details are available elsewhere (Ward & Ward, in press; Ward & Ward, 2006).