seven stages

diff --git a/tex/perceptionaction.tex b/tex/perceptionaction.tex
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--- a/tex/perceptionaction.tex
+++ b/tex/perceptionaction.tex
@@ -1,6 +1,6 @@
 %!TEX root = ../hdrmain.tex
 
-\chapter{The seven stages of computation}
+\chapter{Interaction techniques and devices}
   \epigraph{\lorem}{Auteur}
 
 \begin{Abstract}
@@ -10,21 +10,42 @@
 The design of interactive systems requires deep knowledge of both users and computers.
 Deeper than this, it requires understanding how the user and the interactive system interact with each other.
 
-
 Norman presents his \defword{seven stages of action}, which describes how humans interact with the world~\cite{norman88,norman02}.
 This model is depicted in red on Figure~\ref{fig:extendedaction}.
 The subject starts with establishing a \emph{goal}, which is a high level objective to achieve.
+The purpose of every system is to enable achieving such goals.
 As an example to illustrate the concept, let me present you Jimmy who just returned home after the Christmas holidays.
 His house is cold, and he needs to raise the temperature.
 To achieve this goal he has to formulate \emph{intentions}, such as turning on the radiator on.
-This requires \emph{specifying actions}, like turning a knob and decide how much to turn the knob.
-Last, Jimmy must \emph{execute the actions}.
-
-%They start with a goal, then formulate intentions.
-%Based on this intention they specify a series of actions to perform, then executes them.
-These actions have effects on the world, that they can perceive.
-They interpret it, based on their knowledge and experience.
-Based on this, they make an evaluation of the result of their actions on the world, and refine their goal in accordance.
+This requires \emph{specifying}, then \emph{executing} actions, like turning a knob and decide how much to turn the knob.
+This task is not as trivial as it seems.
+First of all Jimmy identified the possible actions on the radiator, like turning the knob.
+This is what Gibson called an \defword{affordance}~\cite{gibson77}.
+%Objects can have hidden or false affordances.
+%This is the case for a microwave in a flat I rent once, with only one button.
+%I never figured out how to setup time on the display.
+The knob has notches ranging from 0 to 11 painted on the sides.
+They provide \defword{perceived affordances} (also called \defword{signifiers}~\cite{norman08}) that helps Jimmy to know in which direction to turn it.
+Now, Jimmy wants to get warm faster.
+Therefore he turns the knob all the way up to 11, thinking that the radiator will be hotter.
+This is a mistake, because the radiator is either on or off, and (in short) the knob only defines a threshold for switching between these two states.
+It means that the radiator cannot make the room warmer faster.
+This illustrates issues caused by a difference between the designer's model and the user's model.
+An alternative way of conveying an appropriate signifier consists in displaying the target temperature rather than 0-11.
+
+Jimmy's actions have effects on the world, that he can eventually \emph{perceive}.
+In this case he feels the room getting warmer.
+It is unlikely he notices that the room could not get hotter faster.
+However at some point he will notice the room will be too hot because he set it to the maximum value.
+This is an \emph{interpretation} of the results of his actions.
+It is based on both the room temperature he perceives, experience, knowledge, personal taste, etc.
+Jimmy \emph{evaluates} this interpretation and decides the temperature is too hot.
+His new goal is to lower temperature, keeping in mind the initial state.
+
+
+\section{Seven stages of computation}
+
+\cite{vermeulen13}
 
 We can observe that the perception to action sequence is a refinement of O'Regan's \defword{sensorimotor loop}~\cite{oregan01a}.