Interaction is “the reciprocal action between two or more agents”. At the informational level, the one of our interest, interaction is an essential aspect. It’s one of the basic processes through which we acquire relevant information about our environment. The first reactions of most primates in front of a new thing in the environment are observation and interaction. 

Interaction allows us to get information from different perspectives and it’s a nuclear part of learning. The basic idea is to change the environment conditions of the object or agent of our interest in order for it to show another of its facets, possibly hidden in the current state. We exercise a change action in order to achieve a reaction of the object in the new state. The result is a change in our own state. Possibly we identify a new pattern of the object behaviour, that we store in our memory adding up to the knowledge (the list of patterns) about that object.

Interaction, by definition is a reciprocal action. Regardless of who or what initiates the interaction, the result is the modification of the participants’ states. For this reason the simple visualisation of the information contained in a map or a graphic representation, changes our [mental] state but it doesn’t change that of the graphic representation.

The computer is an intrinsically interactive tool, that has made the concept of human-machine interaction to be deeply studied. The graphical user interface (GUI) allow us a much higher level of interaction and learning than the old command line. Unlike graphical representation on paper, computers allow us the interactive creation of graphics that represent large data sets in ways the designer of the visualisation tool didn’t foresee at all.

Online manipulation of the visualisation parameters offers the possibility to change the state of the visualisation itself, incorporating new data, or crossing relations between the existing ones in “a priori” unexpected ways. Interaction makes it possible to explore more possibilities in less time, thus acquiring more patterns of behaviour and, hence, learning more efficiently.

There are two fundamental factors that influence interaction: time and control. 

In this article we'll focus on the first. What lapse has to pass between action and reaction in order for us to speak about interaction?. According to the authors of “Readings in Information Visualisation” there are three levels of interaction located around the 1/10, 1, and 10 seconds time scale.

1. 0,1 seconds, It’s the so called "psychological moment” *. Two events separated by less than this time are fused into one perception due to the fact that the brain’s neural activity cycle has approximately this duration. To get the sensation of animation, the frames of a movie have to appear at higher rates than 10 per second. A stimulus and an action separated by less than this threshold will appear to be linked by a cause and effect relation. If a button changes its appearance in less than this time after clicking the mouse, we’ll have the impression that we have pressed it. In the same way if we move the scroll bar and the data changes accordingly in less than 0.1 seconds it will give the impression that the responsible of this is the movement of the bar.
   
   
2. 1 second. Events that occur at this time scale or less are too quick to respond if we are not prepared for them. A car driver needs 0.7 seconds to react and step the brakes in front of an unforeseen event. An unexpected screen dialogue needs of at least one second in order for the user to prepare and respond. In a communication channel, like two people speaking over the telephone, more than 1 second of silence induces to think that the communication has broken.
   
   
3. 10 seconds (approximately between 5 and 30). Is the typical time needed to complete an interaction task, like choosing a submenu among several possibilities in a spreadsheet or, as the authors of the book suggest, the time it takes to a chess master to make a movement.
   

0,1 second. Is the average duration of the brain activity cycle that flows between the "substantia nigra" (1), that produces dopamine) the basal ganglia (2) and the prefrontal cortex (3). Every "tic" of the clock is the time the nervous impulse needs to complete the cycle and serves as base time to the brain. Drawing inspired in page 160 of "Exploring Conciousness" by Rita Carter.	1 second. Is the approximate reaction time to the unforeseen. The "time for preparation". A car driver needs 0,7 seconds to react to an emergence, like, for example a strong breaking of the next car. Photo courtesy of SUV One Inc	10 seconds. Is the approx. time frame (between 5 and 30 in reality) needed to complete an elementary task, like choosing a submenu among several ones and complete a dialogue. In the image sending a document to the printer. Snapshot of the author's screen.

All of us have experienced some time the confusion that appears when the computer slows down to the point where it is impossible to know which keystroke or mouse click is related with its current reaction. The lag that appears when playing an Internet videogame with saturated lines is another example of the effects of breaking the tuning between human temporal constants and the computer response time. 

Time, in any case , is a fundamental factor of interaction that has to be tuned to the human constants for assimilation and reaction to temporal events.

Next week we’ll speak about control and techniques for interaction.

* Blumenthal, A.L. The process of cognition, Prentice Hall, Englewood Cliffs NJ, 1977 (Available as used book at Alibris)

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