U.S. patent application number 12/520857 was filed with the patent office on 2010-03-04 for assessment of computer games.
This patent application is currently assigned to NEUROINSIGHT PTY. LTD.. Invention is credited to Richard Bernard Silberstein.
Application Number | 20100056276 12/520857 |
Document ID | / |
Family ID | 39562019 |
Filed Date | 2010-03-04 |
United States Patent
Application |
20100056276 |
Kind Code |
A1 |
Silberstein; Richard
Bernard |
March 4, 2010 |
ASSESSMENT OF COMPUTER GAMES
Abstract
A method of improving a computer game, the method including the
steps of: (a) causing a player to play the computer game in which
various game situations are presented to the player during the
course of the game; (b) recording game situation parameters
corresponding to the various game situations of step (a); (c)
determining brain activity of the player during each of the game
situations which are presented to the player; (d) evaluating
effectiveness of the game situation parameters by reference to
brain activities determined in step (c) for each of the game
situation parameters recorded in step (b); and (e) improving the
game by eliminating or modifying those game situations which have
low levels of brain activity as determined in step (d).
Inventors: |
Silberstein; Richard Bernard;
(Victoria, AU) |
Correspondence
Address: |
MASTERMIND IP LAW PC
421-A SANTA MARINA COURT
ESCONDIDO
CA
92029
US
|
Assignee: |
NEUROINSIGHT PTY. LTD.
Hawthorn
AU
|
Family ID: |
39562019 |
Appl. No.: |
12/520857 |
Filed: |
December 22, 2006 |
PCT Filed: |
December 22, 2006 |
PCT NO: |
PCT/AU2006/002004 |
371 Date: |
June 22, 2009 |
Current U.S.
Class: |
463/36 |
Current CPC
Class: |
A63F 13/60 20140902;
A63F 2300/1012 20130101; A61B 5/377 20210101; A61B 5/165 20130101;
A63F 2300/6009 20130101; A63F 13/10 20130101; A61B 5/16 20130101;
A61B 5/245 20210101 |
Class at
Publication: |
463/36 |
International
Class: |
A63F 9/24 20060101
A63F009/24 |
Claims
1. A method of improving a computer game, the method including the
steps of: (a) causing a player to play the computer game in which
various game situations are presented to the player during the
course of the game; (b) recording game situation parameters
corresponding to the various game situations of step (a); (c)
determining brain activity of the player during each of the game
situations which are presented to the player; (d) evaluating
effectiveness of the game situation parameters by reference to
brain activities determined in step (c) for each of the game
situation parameters recorded in step (b); and (e) improving the
game by eliminating or modifying those game situations which have
low levels of brain activity as determined in step (d).
2. A method as claimed in claim 1 wherein the brain activities
determined in step (c) are averaged for each game situation
parameter.
3. A method as claimed in claim 1 or 2 wherein step (a) is
performed by a plurality of players and step (c) includes the steps
of averaging the brain activities of the players.
4. A method as claimed in claim 3 wherein step (c) is carried out
by determining gamma or high frequency EEG or MEG activity.
5. A method as claimed in claim 3 wherein step (c) is carried out
by detecting EEG or MEG activity in the frequency range 8 to 13
Hz.
6. A method as claimed in claim 3 wherein step (c) is carried out
by assessment of the phase of steady state visually evoked
potentials (SSVEP) in EEG signals obtained from the players or by
assessment of steady state visually evoked responses (SSVER) in MEG
signals obtained from the players.
7. A method as claimed in any one of claims 1 to 6 wherein step (c)
includes the steps of placing electrodes at scalp sites to obtain
output EEG signals which enable assessment of: engagement with the
game situations; attraction associated with the game situations;
emotional intensity associated with the game situations; and/or
long term memory encoding associated with the game situations.
8. A method as claimed in claim 7 including the step of applying a
sinusoidally varying visual flicker stimulus to each player during
step (c) to thereby enable calculation of Fourier coefficients from
said output signals to thereby enable calculation of said SSVEP
amplitudes and/or phase differences.
9. A method as claimed in claim 8 wherein said SSVEP amplitude and
phase are calculated by the equations: SSVEP amplitude = ( A n 2 +
B n 2 ) ##EQU00004## SSVEP phase = a tan ( B n A n ) ##EQU00004.2##
where: a.sub.n and b.sub.n are cosine and sine Fourier coefficients
calculated by the equations: a n = 1 S .DELTA. .tau. i = 0 S - 1 f
( nT + i .DELTA. .tau. ) cos ( 2 .pi. T ( nT + i .DELTA. .tau. ) )
##EQU00005## b n = 1 S .DELTA. .tau. i = 0 S - 1 f ( nT + i .DELTA.
.tau. ) sin ( 2 .pi. T ( nT + i .DELTA. .tau. ) ) ##EQU00005.2##
where: a.sub.n and b.sub.n are the cosine and sine Fourier
coefficients respectively where; n represents the nth flicker
stimulus cycle; S is the number of samples per flicker stimulus
cycle; .DELTA..tau. is the time interval between samples; T is the
period of one cycle; f(nT+i.DELTA.r) is the EEG signal (raw or
pre-processed using ICA) obtained from said predetermined scalp
sites; and wherein A.sub.n and B.sub.n are overlapping smoothed
Fourier coefficients calculated by using the equation: A n = i = 1
i = N a n + i / N ##EQU00006## B n = i = 1 i = N b n + i / N
##EQU00006.2##
10. A method as claimed in claim 9 including the steps of:
obtaining EEG signals from a plurality of scalp sites of each
player; and utilising inverse mapping techniques such as BESA, EMSA
or LORETA to produce modified EEG signals which represent activity
in deeper regions of the brain of each subject such as the
orbito-frontal cortex or the ventro-medial cortex.
11. A method as claimed in claim 9 or 10 including the step of
averaging the Fourier coefficients A.sub.n and B.sub.n for a
selected group of players and then calculating the SSVEP amplitudes
and SSVEP phase differences for said group of players.
12. A method as claimed in any one of claims 8 to 11 wherein the
flicker signal is applied only to the peripheral vision of each
player.
13. A method as claimed in claim 12 including the steps of
directing the flicker signal towards the eyes of each player via
first and second screens and wherein each screen includes an opaque
area, and wherein the method further includes the step of
positioning the screens to the relative position of each player
such that said opaque areas prevent said flicker signal impinging
on the fovea of each eye of each player.
14. A method as claimed in claim 13 wherein the opacity of each
screen decreases as a function of distance from its opaque area so
that the intensity of the flicker signal impinging on each retina
of each player decreases in value from the central vision to the
peripheral vision.
15. A method as claimed in claim 14 including the step of applying
a masking pattern to each screen to define the opacity thereof, the
method including the step of applying the pattern in accordance
with a masking pattern function which provides zero or low
gradients for changes in opacity adjacent to its opaque area and
peripheral areas thereof which define parts of the flicker signal
impinging on the peripheral vision of each player.
16. A method as claimed in claim 15 wherein the opaque area of each
screen is circular and wherein the masking pattern function is
selected to be a Gaussian function, so that the opacity P of the
screen is defined by the equation:
P=e.sup.-(r-R).sup.2.sup./G.sup.2 where: r is the radial distance
from the centre of the opaque area; and G is a parameter that
determines the rate of fall-off of opacity with radial distance,
and wherein when r<R, P=1.
17. A method as claimed in claim 16 wherein G has a value in the
range R/4 and 2R.
18. A method as claimed in claim 9 including the step of applying
an electrode to the scalp of each player at a site which is
approximately equidistant from sites O.sub.2, P.sub.4 and T.sub.6,
calculating SSVEP amplitudes and phase differences from EEG signals
from said electrode whereby the output signals indicate each
player's emotional intensity associated with the game situations or
game situation parameters.
19. A method as claimed in claim 10 wherein the step of utilising
inverse mapping determines brain activity in the right cerebral
cortex in the vicinity of the right parieto-temporal junction
whereby the output signals indicate each player's emotional
intensity associated with the game situations or game situation
parameters.
20. A method as claimed in claim 9 including the steps of applying
an electrode to the scalp of each player at the F.sub.3, F.sub.4,
F.sub.p1 and F.sub.p2 sites, calculating SSVEP amplitudes and phase
differences from EEG signals from said electrodes, calculating
values for attraction-repulsion using the equation:
attraction=(a.sub.1*SSVEP phase advance at electrode
F.sub.3+a.sub.2*SSVEP phase advance at electrode
F.sub.p1-a.sub.3*SSVEP phase advance at electrode
F.sub.4-a.sub.4*SSVEP phase advance at electrode F.sub.p2) where
a.sub.1=a.sub.2=a.sub.3=a.sub.4=1.0 whereby said values indicate
each player's attraction or repulsion towards the game situations
or game situation parameters.
21. A method as claimed in claim 10 wherein the step of utilising
inverse mapping determines brain activity in: the right
orbito-frontal cortex in the vicinity of Brodman area 11; the right
dorso-lateral prefrontal cortex in the vicinity of Brodman area 9;
the left orbito frontal cortex in the vicinity of Brodman area 11;
and the left dorso-lateral prefrontal cortex in the vicinity of
Brodman area 9; and calculating a value for attraction-repulsion
using the equation: attraction=(c.sub.1*right orbito-frontal cortex
(in vicinity of Brodman area 11)+c.sub.2*right dorso-lateral
prefrontal cortex (in vicinity of Brodman area 9)+c.sub.3*left
orbito frontal cortex (in vicinity of Brodman area 11)+c.sub.4*left
dorso-lateral prefrontal cortex (vicinity of Brodman area 9)) where
c.sub.1=1, c.sub.2=1, c.sub.3=1, c.sub.4=1, whereby said values
indicate each player's attraction or repulsion towards the game
situations or game situation parameters.
22. A method as claimed in claim 9 including the steps of applying
electrodes to the scalp of each player at F.sub.3, F.sub.4,
P.sub.p1 and F.sub.p2 sites, calculating SSVEP amplitudes and phase
differences from said electrodes, calculating values for engagement
in features of the advertisement by a weighted mean SSVEP phase
advance at said sites using the equation: engagement=(b.sub.1*SSVEP
phase advance at electrode F.sub.3+b.sub.2*SSVEP phase advance at
electrode P.sub.p1+b.sub.3*SSVEP phase advance at electrode
F.sub.4+b.sub.4*SSVEP phase advance at Electrode F.sub.p2) where
b.sub.1=0.1, b.sub.2=0.4, b.sub.3=0.1, b.sub.4=0.4, whereby said
values indicate each player's engagement in the game situations or
game situation parameters.
23. A method as claimed in claim 10 wherein the step of utilising
inverse mapping determines brain activity in: the right orbito
frontal cortex in the vicinity of Brodman area 11; the right
dorso-lateral prefrontal cortex in the vicinity of Brodman area 9;
the left frontal cortex in the vicinity of Brodman area 11; and the
left dorso-lateral prefrontal cortex in the vicinity of Brodman
area 9, calculating SSVEP amplitudes and phase differences from
said modified EEG signals from said electrodes; and calculating a
value for engagement using the equation: engagement=(d.sub.1*right
orbito frontal cortex (in vicinity of Brodman area
11)+d.sub.2*right dorso-lateral prefrontal cortex (in vicinity of
Brodman area 9)+d.sub.3*left orbito frontal cortex (in vicinity of
Brodman area 11)+d.sub.4*left dorso-lateral prefrontal cortex (in
vicinity of Brodman area 9)) where d.sub.1=0.1, d.sub.2=0.4,
d.sub.3=0.1, d.sub.4=0.4, whereby said values indicate each
player's engagement in the game situations or game situation
parameters.
24. A system for assessing entertainment value of a computer game
including: (a) a computer upon which the computer game to be
assessed can be played, the computer being arranged to record game
situation parameters corresponding to various game situations which
occur during playing of the computer game; (b) means for
determining brain activity of the player during each of the game
situations which occur during playing of the computer game; and (c)
means for evaluating the effectiveness of the game situation
parameters by reference to brain activities determined by said
means for determining brain activity for each of the recorded game
situation parameters.
Description
[0001] Computer games and computer based entertainment constitute a
large and rapidly growing economic sector. The development costs
for the more complex internet based multiplayer games are a very
significant investment for even the largest game development
corporations. At present, the likely commercial success of a
computer game is determined by asking people to report their
impressions of the game and then make modifications to enhance the
playability and enjoyment of the games.
[0002] The likely success of any game depends on the extent to
which the player is engaged in the game and also the extent to
which particular situations elicit the desired emotional state,
such as excitement, fear, pleasure etc.
[0003] The most important psychological measure is `engagement`.
The extent to which the game engages the player is given by is
given by the weighted mean brain activity during the initial period
at prefrontal sites described by the expression below:
Engagement=(b.sub.1*brain activity at electrode F.sub.3+b.sub.2*
brain activity at electrode P.sub.p1+b.sub.3*brain activity advance
at electrode F.sub.4+b.sub.4*brain activity at electrode F.sub.p2)
Equation 1 [0004] where: b1=0.1, b2=0.4, b3=0.1, b4=0.4
[0005] If inverse mapping techniques are used, the relevant
expression is:
Engagement=(d.sub.1*brain activity at right orbito frontal cortex
(in vicinity of Brodman area 11)+d.sub.2*brain activity at right
dorso-lateral prefrontal cortex (in vicinity of Brodman area
9)+d.sub.3*brain activity at left orbito frontal cortex (in
vicinity of Brodman area 11)+d.sub.4*brain activity at left
dorso-lateral prefrontal cortex (in vicinity of Brodman area 9))
Equation 2 [0006] where: d.sub.1=0.1, d.sub.2=0.4, d.sub.3=0.1,
d.sub.4=0.4
[0007] Other psychological measures and their brain activity
indicators that are of relevance include:
[0008] Visual attention associated with a given set of situation
parameters is indicated by increased brain activity at left and
right occipital recording sites. In the International 10-20 system
that labels recording sites on the brain, the positions referred to
above correspond to the vicinity of O.sub.1 and O.sub.2. If
activity in deeper parts of the brain are assessed using inverse
mapping techniques such as BESA, EMSE or LORETA in combination with
either electrical or magnetic recordings or SSVEP or SSVER, the
relevant location in the left cerebral cortex is the vicinity of
the left and right occipital lobe.
[0009] The Emotional intensity, associated with a set of situation
parameters is indicated by increased brain activity at right
parieto-temporal region, preferable approximately equidistant from
right hemisphere electrodes O.sub.2, P.sub.4 and T.sub.6 during the
initial period. If inverse mapping techniques are used, the
relevant location in the right cerebral cortex is the vicinity of
the right parieto-temporal junction.
[0010] The extent to which individuals are attracted or repelled by
a game situation associated with a given set of situation
parameters is given by the difference between brain activity at
left frontal/prefrontal and right frontal/prefrontal regions.
Attraction is indicated by a larger activity in the left hemisphere
compared to the right while repulsion is indicated by greater
activity in the right hemisphere compared to the left.
Attraction=(a.sub.1*brain activity recorded at electrode
F.sub.3+a.sub.2*brain activity recorded at electrode
F.sub.p1-a.sub.3*brain activity recorded at electrode
F.sub.4-a4*brain activity recorded at electrode F.sub.p2) Equation
3 [0011] where: a.sub.1=a.sub.2=a.sub.3=a.sub.4=1.0
[0012] A positive value for the Attraction measure is associated
with the participants finding the material attractive and liked
while a negative measure is associated with repulsion or
dislike.
[0013] If inverse mapping techniques are used, the relevant
expression is:
Attraction=(c.sub.1*brain activity at right orbito-brain activity
at frontal cortex (in vicinity of Brodman area 11)+c.sub.2*brain
activity at right dorso-lateral prefrontal cortex (in vicinity of
Brodman area 9)+c.sub.3*brain activity at left orbito frontal
cortex (in vicinity of Brodman area 11)+c.sub.4*brain activity at
left dorso-lateral prefrontal cortex (vicinity of Brodman area 9))
Equation 4 [0014] where: c.sub.1=1, c.sub.2=1, c.sub.3=1,
c.sub.4=1
Determining Computer Game Situation Parameters
[0015] The game situation parameters are a set of digital values
that uniquely identify the situation of the game player. These
parameters will vary with the nature of the game and will also vary
with time as the player progresses through the game. For instance,
in a driving simulation game, the game situation parameters would
comprise the location of the player's car on the simulated track or
landscape, the speed and direction of the players car as well as
the state of the steering wheel, brakes and gears. In an adventure
game, the game situation parameters may include the location and
orientation of the player's representation (avatar) within the
simulated environment such as a building, battleground or
streetscape. In addition, the game situation parameters could
include the status of the avatar such as its capabilities (eg
strength, `magical powers` etc) as well as the location and actions
of other avatars (in multi player games) or computer generated
denizens such as monsters, aliens, wizards. etc. The game situation
parameters change with time and a record of each game situation
parameter as a function of time can be stored as a numerical array
in the game computer memory. While a game is being played, the
relevant game situation parameters are held in computer memory and
when active playing ceases transferred to hard disk memory or
another digital storage medium such as flash memory.
[0016] The game software developers would use standard software
such as C++ or specialized computer games development software such
as DaskBASIC (The Game Creator Ltd, `Rockville`, Warrington Rd,
Lower Ince, Wigan, Lancashire, WN3 4QG, UK) to incorporate the
software to identify and store the game situation parameters while
a game is being played.
[0017] The object of the present invention is to provide a
technique which enables quantitative evaluation of a player's
psychological response to various components of a computer game in
order to be able to improve the computer game.
[0018] According to the present invention there is provided a
method of improving a computer game, the method including the steps
of:
[0019] (a) causing a player to play the computer game in which
various game situations are presented to the player during the
course of the game;
[0020] (b) recording game situation parameters corresponding to the
various game situations of step (a);
[0021] (c) determining brain activity of the player during each of
the game situations which are presented to the player;
[0022] (d) evaluating effectiveness of the game situation
parameters by reference to brain activities determined in step (c)
for each of the game situation parameters recorded in step (b);
and
[0023] (e) improving the game by eliminating or modifying those
game situations which have low levels of brain activity as
determined in step (d).
[0024] The invention also provides a system for assessing
entertainment value of a computer game including:
[0025] (a) a computer upon which the computer game to be assessed
can be played, the computer being arranged to record game situation
parameters corresponding to various game situations which occur
during playing of the computer game;
[0026] (b) means for determining brain activity of the player
during each of the game situations which occur during playing of
the computer game; and
[0027] (c) means for evaluating the effectiveness of the game
situation parameters by reference to brain activities determined by
said means for determining brain activity for each of the recorded
game situation parameters.
[0028] It will be appreciated that the present invention provides a
method that relies on measurement of brain activity rather than
verbal responses to questionnaires or other voluntary feedback in
order to determine an individual player's response to various
components of a computer game. Accordingly, the method of the
invention enables game developers to improve the likely commercial
success of the game by modifying components of the game that are
found to be less engaging.
[0029] In one embodiment, brain activity is measured while subjects
or players take part in the computer game. Simultaneously, the
specific situations encountered by the player are also recorded as
a stream of digital parameters specifying the player situation or
Situation Parameters.
[0030] Typically, 20 to 100 players will play the game while brain
activity and Situation Parameters are recorded. To determine the
brain activity associated with a specific set of situation
parameters or a range of situation parameters, individual player
brain activity is averaged for all points in time where the
recorded situation parameters satisfy certain predetermined
criteria. For each individual player, this will yield a set of mean
brain activity measures associated with each of the situation
parameter criteria. Brain activity for a given situation parameter
criterion is then averaged across all the players or subset of
players.
Measuring Brain Activity
[0031] A number of methods are available for measuring brain
activity. The main feature they must possess is adequate temporal
resolution or the capacity to track the rapid changes in brain
activity. Spontaneous brain electrical activity or the
electroencephalogram (EEG) or the brain electrical activity evoked
by a continuous visual flicker that is the Steady State Visually
Evoked (SSVEP) are two examples of brain electrical activity that
can be used to measure changes in brain activity with sufficient
temporal resolution. The equivalent spontaneous magnetic brain
activity or the magnetoencephalogram (MEG) and the brain magnetic
activity evoked by a continuous visual flicker Steady State
Visually Evoked Response (SSVER).
The Electroencephalogram and Magnetoencephalogram (EEG and MEG)
[0032] The EEG and MEG are the record of spontaneous brain
electrical and magnetic activity recorded at or near the scalp
surface. Brain activity can be assessed from the following EEG or
MEG components.
[0033] A number of methods are available for measuring brain
activity. The main feature they must possess is adequate temporal
resolution or the capacity to track the rapid changes in brain
activity. Spontaneous brain electrical activity or the
electroencephalogram (EEG) or the brain electrical activity evoked
by a continuous visual flicker that is the Steady State Visually
Evoked (SSVEP) are two examples of brain electrical activity that
can be used to measure changes in brain activity with sufficient
temporal resolution. The equivalent spontaneous magnetic brain
activity or the magnetoencephalogram (MEG) and the brain magnetic
activity evoked by a continuous visual flicker Steady State
Visually Evoked Response (SSVER).
1. Gamma or High Frequency EEG or MEG Activity
[0034] This is generally defined as EEG or MEG activity comprising
frequencies between 35 Hz and 80 Hz. Increased levels of Gamma
activity are associated with increased levels of brain activity,
especially concerned with perception. (Fitzgibbon S P, Pope K J,
Mackenzie L, Clark C R, Willoughby J O. Cognitive tasks augment
gamma EEG power. Clin Neurophysiol. 2004: 115:1802-1809.)
[0035] If scalp EEG gamma activity is used as the indicator of
brain activity, the relevant scalp recording sites are listed
above. If EEG gamma activity at the specific brain regions listed
above is used as the indicator brain activity then inverse mapping
techniques such as LORETA must be used (Pascual-Marqui R, Michel C,
Lehmann D (1994): Low resolution electromagnetic tomography: a new
method for localizing electrical activity in the brain. Int J
Psychophysiol 18:49-65).
[0036] If MEG gamma activity at the specific brain regions listed
above is used as the indicator of brain activity, then the
multi-detector MEG recording system must be used in conjunction
with an MEG inverse mapping technique (see Uutela K, Ha{umlaut over
( )}ma{umlaut over ( )}la{umlaut over ( )}inen M, Somersalo E
(1999): Visualization of magnetoencephalographic data using minimum
current estimates. Neuroimage 10:173-180. and Fuchs M, Wagner M,
Kohler T, Wischmann HA (1999): Linear and nonlinear current density
reconstructions. J Clin Neurophysiol 16:267-295).
2. Frequency of EEG or MEG Alpha Activity
[0037] Brain activity may also be indexed by changes in the
frequency of the ongoing EEG or MEG in the alpha frequency range
(8.0 Hz-13.0 Hz). Increased frequency is an indication of increased
activity. The frequency needs to me estimated with high temporal
resolution. Two techniques that can be used to measure
`instantaneous frequency` are complex demodulation (Walter D, The
method of Complex Demodulation. Electroencephalog. Clin.
Neurophysiol. 1968: Suppl 27:53-7) and the use of the Hilbert
Transform (Leon Cohen, "Time-frequency analysis", Prentice-Hall,
1995). Increased brain activity is indicated by an increase in the
instantaneous frequency of the EEG in the alpha frequency
range.
[0038] If the frequency of scalp EEG alpha activity is used as the
indicator of brain activity, the relevant scalp recording sites are
listed above. If the frequency of EEG alpha activity at the
specific brain regions listed above is used as the indicator brain
activity then inverse mapping techniques such as LORETA must be
used (Pascual-Marqui R, Michel C, Lehmann D (1994): Low resolution
electromagnetic tomography: a new method for localizing electrical
activity in the brain. Int J Psychophysiol 18:49-65).
[0039] If the frequency of MEG alpha activity at the specific brain
regions listed above is used as the indicator of brain activity,
then the multi-detector MEG recording system must be used in
conjunction with an MEG inverse mapping technique (see Uutela K,
Ha{umlaut over ( )}ma{umlaut over ( )}la{umlaut over ( )}inen M,
Somersalo E (1999): Visualization of magnetoencephalographic data
using minimum current estimates. Neuroimage 10:173-180. and Fuchs
M, Wagner M, Kohler T, Wischmann HA (1999): Linear and nonlinear
current density reconstructions. J Clin Neurophysiol
16:267-295).
3. SSVEP or SSVER Phase as an Indicator of Brain Activity
[0040] Brain activity may also be indicated by the phase of the
Steady State Visually Evoked Potential (SSVEP) or the Steady State
Visually Evoked Response (SSVER).
[0041] U.S. Pat. Nos. 4,955,938, 5,331,969 and 6,792,304 (the
contents of which are hereby incorporated herein by reference)
disclose technique for obtaining a steady state visually evoked
potential (SSVEP) from a subject. This technique can also be used
to obtain a steady state visually evoked response (SSVER). These
patents disclose the use of Fourier analysis in order to rapidly
obtain the SSVEP and SSVER phase and changes thereto.
[0042] The invention will now be further described with reference
to the accompanying drawings, in which:
[0043] FIG. 1 is a schematic diagram of a system of the
invention;
[0044] FIG. 2 is a schematic view showing in more detail the manner
in which visual flicker stimuli are presented to a subject; and
[0045] FIG. 3 is a graph showing opacity of the screen as a
function of radius.
[0046] FIG. 1 schematically illustrates a system 50 for determining
the response of a subject or a group of subjects to audio-visual
material presented on a video screen 3 and loudspeaker 2. The
system includes a computer 1 which controls various parts of the
hardware and also performs computation on signals derived from the
brain activity of the subject 7, as will be described below. The
computer 1 also holds the images and sounds which can be presented
to one or more subject 7 on the screen 3 and/or through the
loudspeaker 2.
[0047] The subject or subjects 7 to be tested are fitted with a
headset 5 which includes a plurality of electrodes for obtaining
brain electrical activity from various sights on the scalp of the
subject 7. In the event that the SSVER is used, the recording
electrodes in the headset 5 are not used and a commercial MEG
recording system such as the CTF MEG System manufactured by VSM
MedTech Ltd. of 9 Burbidge Street, Coquitlam, BC, Canada, can be
used instead. The headset includes a visor 4 which includes half
silvered mirrors 8 and white light Light Emitting Diode (LED)
arrays 9, as shown in FIG. 2. The half silvered mirrors are
arranged to direct light from the LED arrays 9 towards the eyes of
the subject 7. The LED arrays 9 are controlled so that the light
intensity there from varies sinusoidally under the control of
control circuitry 6. The control circuitry 6 includes a waveform
generator for generating the sinusoidal signal. In the event that
the SSVER is used, the light from the LED array is conveyed to the
visor via a fibre optic system. The circuitry 6 also includes
amplifiers, filters, analogue to digital converters and a USB
interface or a TCP interface or other digital interface for
coupling the various electrode signals into the computer 1.
[0048] A translucent screen 10 is located in front of each LED
array 9. Printed on the screen is an opaque pattern. The opacity is
a maximum in a circular area in the centre of the center of the
screen. Beyond the circular area, the opacity falls off smoothly
with radial distance from the circular area circumference,
preferably, the opacity should fall off as a Gaussian function
described by Equation 5 below. The screen reduces the flicker in
the central visual field thus giving subjects a clear view of the
visually presented material. The size of the central opaque circle
should be such as to occlude the visual flicker in the central
visual field between 1-4 degrees vertically and horizontally.
[0049] If r<R then P=1 [0050] If r.gtoreq.R then P is given by
the equation 1 below.
[0050] P=e.sup.-(r-R.sup.2.sup./G.sup.2 Equation 5 [0051] where P
is the opacity of the pattern on the translucent screen. An opacity
of P=1.0 corresponds to no light being transmitted through the
screen while an opacity of P=0 corresponds to complete
transparency.
[0052] R is the radius of the central opaque disk while r is the
radial distance from the centre of the opaque disk. G is a
parameter that determines the rate of fall-off of opacity with
radial distance. Typically G has values between R/4 and 2R. FIG. 3
illustrates the fall-off of opacity with radial distance from the
centre of the disk. In FIG. 3, R=1 and G=2R.
[0053] The computer 1 includes software which calculates SSVEP or
SSVER amplitude and phase from each of the electrodes in the
headset 5 or MEG sensors.
[0054] Details of the hardware and software required for generating
SSVEP and SSVER are well known and need not be described in detail.
In this respect reference is made to the aforementioned United
States patent specifications which disclose details of the hardware
and techniques for computation of SSVEP. Briefly, the subject 7
views the video screen 3 through the special visor 4 which delivers
a continuous background flicker to the peripheral vision. The
frequency of the background flicker is typically 13 Hz but may be
selected to be between 3 Hz and 50 Hz. More than one flicker
frequency can be presented simultaneously. The number of
frequencies can vary between 1 and 5. Brain electrical activity
will be recorded using specialized electronic hardware that filters
and amplifies the signal, digitizes it in the circuit 6 where it is
then transferred to the computer 1 for storage and analysis.
[0055] When using the SSVEP, brain electrical activity is recorded
using multiple electrodes in headset 5 or another commercially
available multi-electrode system such as Electro-cap (ECI Inc.,
Eaton, Ohio USA). When using the SSVER, commercial MEG recording
system such as the CTF MEG System manufactured by VSM MedTech Ltd
may be used. The number of electrodes or magnetic recording sites
is normally not less than 8 and normally not more than 128,
typically 16 to 32.
[0056] Brain electrical activity at each of the electrodes is
conducted to a signal conditioning system and control circuitry 6.
The circuitry 6 includes multistage fixed gain amplification, band
pass filtering and sample-and-hold circuitry for each channel.
Amplified/filtered brain activity is digitized to 16-24 bit
accuracy at a rate not less than 300 Hz and transferred to the
computer 1 for storage on hard disk. The timing of each brain
electrical sample together with the time of presentation of
different components of the audio-visual material are also
registered and stored to an accuracy 10 microseconds. The
equivalent MEG recording system that is commercially available
performs the same functions.
SSVEP and SSVER Amplitude and Phase
[0057] The digitized brain electrical activity
(electroencephalogram or EEG) brain magnetic activity (MEG)
together with timing of the stimulus zero crossings enables one to
calculate the SSVEP or SSVER elicited by the flicker at a
particular stimulus frequency from the recorded EEG or MEG or from
EEG or MEG data that has been pre-processed using Independent
Components Analysis (ICA) to remove artefacts and increase the
signal to noise ratio. [Bell A. J. and Sejnowski T. J. 1995. An
information maximisation approach to blind separation and blind
deconvolution, Neural Computation, 7, 6, 1129-1159; T-P. Jung, S.
Makeig, M. Westerfield, J. Townsend, E. Courchesne and T. J.
Sejnowskik, Independent component analysis of single-trial
event-related potential Human Brain Mapping, 14(3):168-85,
2001.]
[0058] Calculation of SSVEP or SSVER amplitude and phase for each
stimulus cycle for a given stimulus frequency. Calculation
accomplished used Fourier techniques using Equations 6 and 7
below.
a n = 1 S .DELTA. .tau. i = 0 S - 1 f ( nT + i .DELTA. .tau. ) cos
( 2 .pi. T ( nT + i .DELTA. .tau. ) ) b n = 1 S .DELTA. .tau. i = 0
S - 1 f ( nT + i .DELTA. .tau. ) sin ( 2 .pi. T ( nT + i .DELTA.
.tau. ) ) Equation 6 ##EQU00001##
[0059] Calculation of SSVEP Fourier components where a.sub.n and
b.sub.n are the cosine and sine Fourier coefficients respectively.
n represents the nth stimulus cycle, S is the number of samples per
stimulus cycle (typically 16 samples per cycle), .DELTA..tau. is
the time interval between samples, T is the period of one cycle and
f(nT+i.DELTA..tau.) is the EEG or MEG signal (raw or pre-processed
using ICA).
SSVEP amplitude = ( A n 2 + B n 2 ) or SSVER amplitude = ( A n 2 +
B n 2 ) SSVEP phase = a tan ( B n A n ) or SSVER phase = a tan ( B
n A n ) Equation 7 ##EQU00002##
[0060] Where A.sub.n and B.sub.n are overlapping smoothed Fourier
coefficients calculated by using Equation 4 below.
A n = i = 1 i = N a n + i / N B n = i = 1 i = N b n + i / N
Equation 8 ##EQU00003##
[0061] Amplitude and phase components can be calculated using
either single cycle Fourier coefficients (a.sub.n and b.sub.n) or
coefficients that have been calculated by smoothing across multiple
cycles (A.sub.n and B.sub.n).
[0062] Equations 7 and 8 describe the procedure for calculating the
smoothed SSVEP or SSVER coefficients for a single subject. For
pooled data, the SSVEP or SSVER coefficients (A.sub.n and B.sub.n)
for a given electrode are averaged (or pooled) across all of the
subjects or a selected group of subjects.
[0063] As the number of cycles used in the smoothing increases, the
signal to noise ratio increases while the temporal resolution
decreases. The number of cycles used in the smoothing is typically
in excess of 5 and less than 130.
[0064] The above equations apply to scalp SSVEP data as well as
brain electrical activity inferred at the cortical surface adjacent
to the skull and deeper regions. Activity in deeper regions of the
brain such as the orbito-frontal cortex or ventro-medial cortex can
be determined using a number of available inverse mapping
techniques such as EMSE (Source Signal Imaging, Inc, 2323 Broadway,
Suite 102, San Diego, Calif. 92102, USA) and LORETA (Pascual-Marqui
R, Michel C, Lehmann D (1994): Low resolution electromagnetic
tomography: a new method for localizing electrical activity in the
brain. Int J Psychophysiol 18:49-65). If the SSVER amplitude or
phase changes at the specific brain regions listed above are used
as the indicator of brain activity, then the multi-detector MEG
recording system must be used in conjunction with an MEG inverse
mapping technique (see Uutela K, Ha{umlaut over ( )}ma{umlaut over
( )}la{umlaut over ( )}inen M, Somersalo E (1999): Visualization of
magnetoencephalographic data using minimum current estimates.
Neuroimage 10:173-180. and Fuchs M, Wagner M, Kohler T, Wischmann H
A (1999): Linear and nonlinear current density reconstructions. J
Clin Neurophysiol 16:267-295).
[0065] While participants are playing the computer game, the visual
flicker is switched on in the visor 8 and brain electrical activity
is recorded continuously on the computer 1. At the end of the
recording stage, the SSVEP or SSVER amplitude and phase are
separately calculated for each individual.
EXAMPLE
[0066] In the following example, a computer game development
company needs to assess the psychological impact of a computer game
under development. 20 to 100 participants drawn from the target
market for the game are recruited into the study. Brain activity is
then recorded while the participants play the computer under
development. Each participant plays the game on an individual
computer located in a booth to reduce distraction. To record brain
activity, the headsets 5 are placed on their heads and the visors 4
are placed in position and adjusted so that for each participant
the foveal block by the screens 10 prevents the appearance of the
flicker over the central portion of the screen 3.
[0067] Once brain activity and situation parameters have been
recorded for all game playing participants, each participants brain
activity is averaged when the situation parameters satisfy certain
criteria. As an example, one such criterion could be a specific
geographical location and speed prior to a collision in a racing
car game. Alternatively, in a war game, it could be a particular
battlefield location when the player is under attack from more than
three enemy soldiers. Each game would therefore have a unique set
of situation parameters criteria that reflected the components of
the game where the game developer required player psychological
information. Brain activity measured for the various situation
parameters criteria can then be averaged across all the players to
obtain a representative response for each criterion or set of
specified situation parameters.
[0068] While the most important psychological parameters are
engagement and attention, other parameters may also be important at
various portions of the game. For example, emotional intensity may
be important in certain components of the game while long-term
memory may be important where information needs to be remembered or
where advertising takes place in the game. The psychological
parameters can be measured using the techniques described earlier
and these can be plotted graphically for the various game situation
parameters of interest. The game developer can then determine which
of the game parameters has a relatively low entertainment value.
These parts of the game could therefore be eliminated or modified
to make them more interesting so as to achieve higher measures of
engagement and attention or other psychological responses of
interest.
[0069] The accuracy of the assessment can be improved by measuring
the brain activity of the players against reference levels. One
convenient way to do this would be to average the brain activity
for each player during the whole game and then compare the brain
activity during the game situations of interest to the average game
level. This provides a more accurate measure of the players'
psychological responses to the game situations of interest.
Alternatively, prior to commencement of a game, each of the players
could be presented with a series of still images or the like
together with musical accompaniment and brain activities measured
in the usual way during this reference period. Brain activities can
then be assessed against the reference levels which also provides
increased accuracy. Reference periods presented in this way also
provide an opportunity for comparisons to be made between game
situations of different games rather than game situations within a
single game.
[0070] Many modifications will be apparent to those skilled in the
art without departing from the spirit and scope of the
invention.
* * * * *