%!TEX root = ../hdrmain.tex
-\chapter{The sense of touch}
+\chapter{The sense of touch}\label{chap:output}
\epigraph{\lorem}{Auteur}
\begin{Abstract}
};
\draw [->, -stealth', thick] (info.north) -- (software.south) node [midway, left] {Data};
\draw [->, -stealth', thick] (software.north) -- (mechanics.south) node [midway, left] {Command};
- \draw [->, -stealth', thick] (mechanics.east) -- (sensory.west) node [midway, above] {Mechanical };
+ \draw [->, -stealth', thick] (mechanics.east) -- (sensory.west) node [midway, above] {Physical };
\draw [->, -stealth', thick] (mechanics.east) -- (sensory.west) node [midway, below] { effect};
\draw [->, -stealth', thick] (sensory.south) -- (cognitive.north) node [midway, right] {Sensation};
\draw [->, -stealth', thick] (cognitive.south) -- (perception.north) node [midway, right] {Interpretation};
Other systems sense forces and compute an output motion, this is called \defword{admittance control}~\cite{vanderlinde02}.
This is less used because forces are harder to measures, especially if precision is required.
The advantage of such systems is their much higher stiffness than inductance systems.
-
-EMS \cite{tamaki10}
+It is also worth mentioning Electrical Muscular Stimulation (EMS) which directly stimulates muscles with electrical signals~\cite{tamaki10}.
There are many ways to compute tactile signals, especially due to the diversity of actuation mechanisms and associated effects.
Vibrotactile feedback is certainly the most common type of haptic feedback, because of its low price and simplicity.
Finally, there are non-contact tactile technologies that transmit tactile feedback through air.
The first technique uses an array of ultrasound actuators.
-The interferences of ultrasound waves create a stress field that triggers the mechanoreceptors of the skin~\cite{hoshi10,carter13}
+The interferences of ultrasound waves create a stress field that triggers the sense of touch~\cite{hoshi10,carter13}
The second technique uses air vortexes~\cite{guptas13,sodhi13}.
The displacement of a large membrane inside a box moves the air inside, which can escape trough a small circular hole.
The vortex is created with the pressure, and moves forward on several meters before dissipating.
\paragraph{Sense of touch}
+The objective when producing a physical effect with a haptic system is to stimulate the users' sense of touch.
+On Figure~\ref{fig:hapticpath}, I separate the pure sensing part from the interpretation part.
+The body has sensors in the skin, muscles, tendons and articulations~\cite{bolanowski88}.
+These sensors are different type of nerves and similarly to electronic sensors they transform physical effects into electric signals.
+This document will not cover this in detail.
+The interested reader will find explanations in many Ph.D. manuscripts about haptics~\cite{brown07,crossan03,hoggan10,oakley03}, including mine~\cite{pietrzak08}.
+We will just mention cornerstone studies about the perception of touch that established the limits of tactile perception~\cite{goff67}, which depend on body part, sex and laterality~\cite{weinstein68}.
+In particular authors established the range of frequencies humans can perceive (roughly up to 1000Hz), with a peak perception around 250Hz.
+This study is the motivation why most of vibrotactile systems use a 250 Hz signal, sometimes modulated with another frequency~\cite{brown06}.
+My opinion on this choice is that other frequencies provide different, and interesting sensations.
+They just require a higher amplitude to be perceivable.
+However the amplitude produced with usual vibrotactile systems is sufficient for a large range of frequencies.
+%This is not necessarily an issue on a design point of view because high amplitude vibrations are uncomfortable anyway.
+This is why we typically used different frequencies in our studies~\cite{gupta16,gupta17}.
+
+The perception of touch is however not only a matter of received signal.
+Gibson showed that people are more efficient at tactile exploration with active touch~\cite{gibson62}.
+This means the brain combines sensations with other information, including exploratory movements that resulted in these sensations.
+Given the diversity of touch sensations: weight, shape, temperature, etc., Lederman and Klatzky describe specific exploratory procedure that enable people to perceive these types of sensations~\cite{lederman96}.
+This chapter will not get into details regarding the relation between action and perception since we will cover this specific topic in chapter~\ref{chap:loop}.
+
+Independently of active touch, our perception of haptic signals is an interpretation of the brain.
+For example people may perceive only one vibration while there are two distinct stimulation if they are too close in space~\cite{weinstein68} or time~\cite{goodfellow34}.
+We can use such interpretations to create tactile illusions.
+For example the funneling illusion, also called phantom sensations enables to create a virtual vibration in between two points\cite{alles70,vonbekesy58}.
+To do so, one must place two actuators, one at each end.
+The amplitude of the signal on both actuators is a ratio corresponding to the desired position of the virtual vibration.
+For example let $A$ be the maximum amplitude and two actuators $a$ and $b$ placed $4cm$ apart.
+If the amplitude of actuator $a$ is $\frac{A}{4}$ and the amplitude of actuator $b$ is $\frac{3A}{4}$, then the users feel a vibration between $a$ and $b$, $1cm$ away from $a$ and $3cm$ away from $b$.
+Tactile saltation, also called the cutaneous rabbit illusion, gives the illusion of a sequence of equally spaced vibration~\cite{geldard72}.
+The tactile stimulation however is a repeated vibration on a smaller subset of locations.
+For example with three actuators $a$, $b$ and $c$ equally spaced on a straight line, the stimulation is three vibrations on $a$, three on $b$b, and three on $c$.
+The person feels nine equally spaced stimulations between $a$ and $c$.
+Israr \etal combined both funneling and saltation to produce 2D tactile motions, not only in straight line but also on curves~\cite{israr11}.
\section{Research questions}
+The haptic rendering pipeline illustrates the multidisciplinary aspect of such research.
+It also reveals the many pitfalls at all levels that can make users perceive something different than what was intended.
+The software controller must encode information in an appropriate way.
+Information can get lost
+The physical effect resulting from command sent to the electro-mechanical
+
+%The software controller provides users with \defword{modalities}, or \defword{interaction techniques}, which are combinations of a a device (the electro-machanical system) and an interactive language~\cite{nigay95}.
+
%Leverage the sense of touch to improve interaction.
Many places where information can get lost: command resolution, non-linear mechanical effect, bad contact between device and user, effect out of perceptual range, haptic illusions.
+ Replicability
+
+ Home made device, inter-personal differences, random differences
+
+ Ecological validity
+
+ Co-design of devices: human factors guide the design, and the technical limitations shape the vocabulary
-\subsection{Towards a haptic semiology}{}
+%\subsection{Towards a haptic semiology}{}
-Lack of Bertin-like haptic semiology \cite{bertin83} \texttt{=>} diversity of sensations, stimulation mechanisms, haptic variables
+%Lack of Bertin-like haptic semiology \cite{bertin83} \texttt{=>} diversity of sensations, stimulation mechanisms, haptic variables
%\cite{deroy12}
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