Articles:Physiological Measures for Game Evaluation
From unthinkMedia
Physiological signals allow access to "contextually-relevant" data. This allow for an objective outlook of the users experience, and most importantly doesn't impact the the player's gameplay experience.
Contents
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Current Testing Methods
What to Choose
Choosing the right method depends on what you would like to measure, and what you setting could support.
- What do I want to know about the user experience?
- Will using this sensor intrusively impact the user's game experience?
- Will using this sensor be impacted by the user's game play? (Wii, Kinect...)
Psychological
Arousal
- increase Galvanic Skin Response
- increase Heart Rate
- increase respiration
- decrease in blood volume pulse
Mental Effort
depending on setting
- decrease heart variability rate
- increase pupil dilation
- increase jaw clinching (EMG)
- increase brow raising (EMG)
- increase respiration rate
- decrease respiration variability rate
Positive vs. Negative Emotion
the valence of an emotion
- facial muscle EMG over brow and cheek
- hear rate
- respiration irregularity
- pupil diameter
Sensitivity
Movement
- Blood Volume Pulse
- Galvanic Skin Response
- Respiration via Stretch Sensor
Physical Activity
Most sensors are sensitive to physical activity... be careful
Individual Differences
- between individual users
- between the same user at different times of the day (Use Normalization)
Electrodermal Activity
Galvanic Skin Response (GSR)
Also known as the psychgalvanic reflex, measures both skin resistance and conductance, however the conductance is the norm. This technology is also use in "lie detectors"
How
- As the sweat rises to the skin so does skin conductance, even before the it reaches the skin.
- simple circuit with 2 contact points on the skin.
Readings
There are two components to GSR
- tonic base line: This is the "general" conductance of the skin
- short term phasic response
Application
Typically these sensor are place on:
- Hands
- Soles of Feet
Types of Response
Boucsein, 1992
- Emotional
- Cognitive
- Stress
- Mental workload
Lang, 1995
- Anger
- Fear
Factors
- Age
- Sex
- Temperature
- Humidity
- Menstrual Cycle
- Time of Day
- Sweating through exercise
- Deep breathing
Cardiovascular Sensors
Blood Pressure (BP)
The pressure that blood pushes through veins.
Factors
- Age
- Diet
- Posture
- Weight
- Setting (Clinical/Normal)
- Stress
Limitations
- Can't take more then one reading per minute (automated)
- Not very good for real time gaming situations.
Blood Volume Pulse (BVP)
Amount/Timing of blood flowing an individual using a plethysmograph. The basic function is the placement of a photocell over an area of tissue, such as a finger, and shining a light from the other side. The light bounces through the tissue, and the amount of light that is able to pass through to the photocell is measured.
Not quite clear on how the inflatable cuffs work,however since these cuffs are used it makes game play difficult.
Heart Rate (HR)
The number of contractions of the heart in one minute of time. This could be measure by a variety of methods.
sdf
- positive/negative emotion (Papillo and Shapiro, 1990)
- anger/fear (Papillo and Shapiro, 1990)
Heart Rate Variability (HRV)
The number of oscillations of the interval between heart beats.
Electrocardiography (EKG)
Measures the electrical activity of the heart, using surface electrodes.
can measure:
- heart rate
- inter-beat intervals
- Heart rate variability (HRV)
- Respiratory Sinus arrhythmia (RSA)
Respiratory Sensors
Measures the volume that an individual intakes in their lungs. There are 2 categorizations:
- Tidal Volume
- volume displaced in single breath
- duration of inspiration
- duration of expiraion
- total cycle duration
- Minute Volume(VMIN)
- Tidal Volume / Respiration Rate
- indicates the volume displace in a minute
Muscle Sensors
Electromyography (EMG)
Measures muscle activity by detecting surface voltage.
used to detect
- mental effort
- facial gestures
Effects are stronger when averaged over a group.
Disadvantages
- reading could be interfered with talking, smiling and laughing.
- hair
Needles an alternative, but not very practical.
Alternative Sensors
Electroencephalography (EEG)
Records electrical activity on the scalp related to cortical activity.
Has been successfully be used as input for a game (Hjelm, 2003)
useful for:
- measuring emotion
- event related potential (ERPs) are time linked to specific stimuli.
Research: FUGA Research Project
Pupillometry
The study of pupil dilation.
useful for:
- mental effort
disadvatages:
- changes in light
- changes in spatial patterns
- changes in color
- target motion
Issues
Data collection is complex, and there is no plug-and-play solution. The data is also easily influenced by every day issues such as stress, tiredness, and even the amount of coffee that participant consumed. Many of these factors could change day to day, making it difficult to have a consistent base line reading to compare too.
Sensors data is also not to friendly with removing and reapplying the data. Different parts of the body could output dramatically different results.
People are different
Data issues
Sensor Errors
For minor random fluctuations you Will need to look up "standard signal processing" information
- smoothing using moving average window: This averages out X number of frames, for a predetermined amount of time
- filtering using low pass filter: This is more difficult but allows you to identify quick spikes and remove certain frequencies.
Advantages
- Reduce the time to test video, by investigating peaks in data, and attaching those peaks to a timecode.
Inferring a Users Emotional State
For more info look up Mandryk and Atkins (2007)(2006)
requires:
- signal processing
- experiment design
- psychophysiology
- theories of emotion
