Wednesday, October 19, 2011

Object Thinking - Objects have actions

This post follows on from Object Thinking - Objects: a neurological basis

The paper being reviewed is Micro-affordance: The potentiation of components of action by seen objects (Ellis and Tucker, 2000)[1]
The paper focuses on two experiments. The first is concerned with power and precision micro-affordance, and the second with wrist rotation micro-affordance.

In the first experiment the participants were told to memorise objects as they were shown them. They were then tested on the objects halfway through the experiment and at the end. During the memorisation phase, whenever they heard a tone, the participant was to either squeeze a cylindrical button with their whole hand, or pinch a small button between their index finger and thumb.

The type of grip response would be dependant on the type of tone; high or low. So there were two mappings known to the participants: high – large grip, low – small grip, and high – small grip, low – large grip. There were also two unknown mappings: high – large object, low – small object, and high – small object, low large object.

Each participant was assigned one mapping from each of the two groups and this was sustained throughout the experiment.

In the results from the experiment there was a statistically significant positive correlation between grip type and object type.

The second experiment was set up much the same as the first. The differences were that instead of large or small grips, the participant would make clockwise or anticlockwise wrist rotations dependant on tone, and the objects were categorised as ones more easily grasped with an anticlockwise or clockwise wrist rotation.

The results showed a statistically significant positive correlation between wrist rotation and object type.

The paper classifies micro-affordance (MA) as the state of an observer that gives rise to stimulus-response compatibility (SRC) between what the viewer sees and what actions they perform regardless of their intention. The theory is meant as a solution to the symbol grounding problem. (The reference to this problem in the paper is Harnad, 1990[2].)

The paper explains that SRC is demonstrated in many previous experiments, by various researchers, in forced choice reaction time tests. For example an advantage is gained when reaching for something on the left with the left hand, and similarly for the right. In fact an advantage is gained even in non-reaching tasks, where the location of the stimulus gives an advantage when it is on the same side as the response, this is known as the Simon Effect.

Previous experiments by Ellis and Tucker show that location is not the only action related feature encoded in this way.

This preparedness for action is thought to be a coordination of the what and where pathways in the brain.

The paper reports that the theoretical implications of the results of the study are:
  1. MA are different from Gibsonian affordance in that they suggest the affordance is encoded in the viewer's nervous system (not the object being viewed), they only apply to grasping, and only grasping appropriate to the object.
  2. SRC works because what is being responded to is unrelated to what is causing the compatibility effect. SRC theories suggest that stimulus → response options elicit particular mental codes, so the location of an object elicits a left or right handed response. MA, however, can be evoked without evoking a coherent action.
    This means that MA should interfere with SRC experiments.
    SRC effects have been modelled as ecological relations between visual properties and actions. They have also been modelled as effect codes that can be combined into whole actions.
    MA and these two approaches share the assumption that a compatibility effect arises from visual objects and possible, real-world actions that can be performed on them.
    MA diverges from the ecological approach by retaining representation of objects, and from effect codes by having a direct connection between vision and action. MA diverges from both because it states that actions are potentiated whenever an object is seen, regardless of the intention of the viewer.
  3. Developmentally, MA fits in well with the popular theory of Neural Darwinism. Development of adaptive behaviours requires integration of sensory and motor processes. The paper proposes learning coordinated actions result from gradual adaption of the neuron groups involved. This leads to coupling of motor and sensory systems.
    The implication of the experiments is that MA reflect the involvement of the motor components of the global mapping, which have come to represent visual objects.

So what does this tell us about how natural object thinking is? Object thinking requires that you understand the objects your are working with in terms of the behaviours that they can perform. You need to be able to create your objects so that discovering what behaviours are available is intuitive — i.e. when others come to your API they aren't spending hours going through the documentation, they can just get on and use it.

Ellis and Tucker show that the brain is well suited to understanding and preparing for expected behaviours. When we see an object, we immediately know the actions that the object has available, and are primed to use them.

This implies that once we have a good understanding of a problem domain, we should be able to model the behaviours of the objects in the domain intuitively, and anyone else with a good understanding of the problem domain will be able to intuitively discover each object and its behaviours.

The behaviour driven aspects of object thinking are intrinsic to how the human mind works at the brain level.

The next section deals with anthropomorphism, why OT needs it and where it comes from: Object Thinking - Anthropomorphism.

[1] Micro-affordance: The potentiation of components of action by seen objects; Rob Ellis, Mike Tucker. British Journal of Psychology (2000), 91, 451-471
[2] Harnad, S. (1990). The symbol grounding problem. Physica D, 42, 335±346. (As sited in [1])