WO2006125246A1

WO2006125246A1 - Brain correlates of deception and criminal behaviour

Info

Publication number: WO2006125246A1
Application number: PCT/AU2006/000628
Authority: WO
Inventors: Richard Bernard Silberstein
Original assignee: Sspt Pty. Ltd.
Priority date: 2005-05-25
Filing date: 2006-05-12
Publication date: 2006-11-30
Also published as: GB0724551D0; GB2441275A

Abstract

A method of detecting an untrue or deceptive response of a participant to a cognitive task, the method including the steps of: presenting to the participant a group of cognitive tasks including control tasks and test tasks; detecting brain response signals from the participant during presentation of the group of cognitive tasks; calculating SSVEP amplitude, phase and/or coherence from the brain response signals; comparing SSVEP amplitude, phase and/or coherence from the controlled tasks to SSVEP amplitude, phase and/or coherence from the test tasks; and determining that the subject is giving an untrue or deceptive response if there is a predetermined change in SSVEP amplitude, phase or coherence associated with the test tasks.

Description

BRAIN CORRELATES OF DECEPTION AND CRIMINAL BEHAVIOUR

The present invention relates to brain correlates of deception and criminal behaviour.

There is a need to be able to determine whether individuals are answering questions deceptively. The ability to determine whether individuals are answering deceptively has applications in fields as diverse as the selection of staff to manage critical facilities (e.g. nuclear power plants), determining whether prisoners charged with serious offences can be safely paroled, and national security where there may be a need to identify individuals likely to participate in acts of terrorism. There is also a need to be able to determine whether an individual recognises an image or sound which is known to the individual from his own past activity. Also, there is a need to be able to determine whether the individual has interest in subject matter related to criminal, anti-social or terrorist activity.

A number of techniques are currently available or under development to address this issue. These include the "polygraph" or lie detector as well as more recent techniques that rely on changes in brain activity. Dr. Lawrence Farwell of Brain Fingerprint Laboratories Inc. utilises an electrical signal recorded from the scalp 300-600 msec after the image of an object or word is presented. This signal, generally known as P300, is larger for images that are recognised compared to novel or unrecognised objects. The capacity to identify images that are recognised by an individual has been developed into a criminal investigative technique known as "guilty knowledge" detection. This technique has not been widely accepted as it depends on the existence of specific information known only to the investigator and the individual under investigation. Furthermore, the technique cannot be used generally to determine whether individuals are answering questions untruthfully.

Functional magnetic resonance imaging (fMRI) has also been used to investigate brain activity correlates of deception. Daniel Langleben of the University of Pennsylvania

(Langleben DD₅ Schroeder L, Maldjian JA, Gur RC, McDonald S, Ragland JD, O'Brien CP, Childress AR. Brain activity during simulated deception: an event-related functional magnetic resonance study. Neuroimage. 2002 Mar; 15(3):727-32) has reported that the anterior cingulate cortex and the superior frontal gyrus are more strongly activated during deception compared to answering truthfully. While this is an interesting finding, it is unlikely that fMRI techniques will be widely used to assess truthfulness. The cost and bulk of fMRI machines, let alone the tendency for people to experience claustrophobia in fMRI machines makes this technology impractical. Optical methods are also being used to measure brain activity during deception in a number of research studies. Dr. Britton Chance at the University of Pennsylvania is using near-infrared photons to detect changes in frontal blood flow during deception. The major weakness of this approach is that the brain blood flow changes may be too slow to capture rapid changes associated with deception.

The invention utilises the technique known as Steady State Probe Topography (SSPT) to measure brain electrical activity while a participant under investigation is answering questions where questions may be presented by an authorised individual orally or presented in audible or written form by a computer, alternatively an audio video segment may be used instead of questions.

United States Patent Nos. 4,955,938 and 5,331,969 (the contents of which are hereby incorporated herein by reference) disclose technique for obtaining a steady state visually evoked potential (SSVEP) from a participant. These patents disclose the use of Fourier analysis in order to rapidly obtain the SSVEP's and changes thereto. It is now appreciated that these techniques can be utilized to monitor brain activity associated with deception. The present invention utilizes SSPT, a brain imaging technique based on the brain's response to a continuous visual flicker or the SSVEP to examine changes in the activity in various brain regions while the participant under investigation is required to answer questions truthfully. It is suggested that a deceptive answer and the times when the participant under investigation is selecting a deceptive response will be characterized by specific changes in SSVEP amplitude, SSVEP phase and SSVEP coherence that are not apparent during a truthful response. Different specific changes would also be apparent when the participant recognises an image or sound or has interest in particular subject matter.

In addition, SSVEP amplitude, phase and coherence at various brain regions can be used to determine the psychological response of a participant under investigation to audiovisual segment associated with previous criminal or terrorist activity of the participant under investigation. Such responses will give an indication of the participant's psychological responses and the likely probability of re-offending, committing a related offence or carrying out an act of terrorism.

More particularly, the techniques of the invention can be used in a number of different fields including, but not limited to:

(i) detection of deception;

(ii) detection of an intention to deceive; (iii) detection of recognition by a participant of an image or sound;

(iv) detection of an interest of a participant in subject matter from which can be inferred an intention to commit or recommit antisocial behaviour such as criminal acts and/or terrorist acts.

More particularly, the invention provides a method of detecting an untrue or deceptive response of a participant to a cognitive task, the method including the steps of: presenting to the participant a group of cognitive tasks including control tasks and test tasks; detecting brain response signals from the participant during presentation of said group of cognitive tasks; calculating SSVEP amplitude, phase and/or coherence from said brain response signals; comparing SSVEP amplitude, phase and/or coherence from said controlled tasks to SSVEP amplitude, phase and/or coherence from said test tasks; and determining that the subject is giving an untrue or deceptive response if there is a predetermined change in SSVEP amplitude, phase or coherence associated with the test tasks.

The invention also provides a method of determining whether a participant recognises a test image, the method including the steps of: presenting to the participant a group of images including control images and test images; detecting brain response signals from the participant during presentation of said group of images; calculating SSVEP amplitude, phase and/or coherence from said brain response signals; comparing SSVEP amplitude, phase and/or coherence from said control images to SSVEP amplitude, phase and/or coherence from said test images; and determining that the participant does recognise the image if there is a predetermined change in SSVEP amplitude, phase and/or coherence associated with the test images.

The invention also provides a method of determining whether a participant recognises a test sound, the method including the steps of: presenting to the participant a group of sounds including control sounds and test sounds; detecting brain response signals from the participant during presentation of said group of sounds; calculating SSVEP amplitude, phase and/or coherence from said brain response signals; comparing SSVEP amplitude, phase and/or coherence from said control sounds to

SSVEP amplitude, phase and/or coherence from said test sounds; and determining that the participant does recognise a test sound if there is a predetermined change in SSVEP amplitude, phase and/or coherence associated with that test sound. The invention also provides a method of determining if a participant has an interest in particular subject matter, the method including the steps of: presenting to the participant audio visual material including neutral subject matter and particular subject matter, detecting brain responses from the participant during presentation of said audio visual material; calculating SSVEP amplitude, phase and/or coherence from said brain response signals; comparing SSVEP amplitude, phase and/or coherence from said neutral subject matter to SSVEP amplitude, phase and/or coherence from said particular subject matter; and determining that the participant does have an interest in the particular subject matter if there is a predetermined change in SSVEP amplitude, phase and/or coherence associated with the particular subject matter.

The invention also provides apparatus for detecting an untrue or deceptive response of a participant to a cognitive task, the apparatus including means for presenting to the participant a group of cognitive tasks including control tasks and test tasks; detecting means for detecting brain response signals from the participant during presentation of said group of cognitive tasks; calculating means for calculating SSVEP amplitude, phase and/or coherence from said brain response signals; comparing means for comparing SSVEP amplitude, phase and/or coherence from said control task to SSVEP amplitude, phase and/or coherence from said test tasks in order to determine if the responses to the test tasks are or are likely to be untrue or deceptive.

The invention also provides apparatus for determining whether a participant recognises a test image, the apparatus including: display means for presenting to a participant a group of images including control images and test images; detecting means for detecting brain response signals from the participant during presentation of the group of images; calculating means for calculating SSVEP amplitude, phase and/or coherence from said brain response signals, comparing means for comparing SSVEP amplitude, phase and/or coherence from said control images to said SSVEP amplitude, phase and/or coherence from said test images in order to determine whether or not the participant does recognise the image if there is a predetermined change in SSVEP amplitude, phase and/or coherence associated with that test image.

The invention also provides apparatus for determining whether a participant recognises a test sound, the apparatus including: a loudspeaker for presenting to the participant a group of sounds including control sounds and test sounds; detecting means for detecting brain response signals from the participant during presentation of said group of sounds; calculating means for detecting SSVEP amplitude, phase and/or coherence from said brain response signals; and comparing means for comparing SSVEP amplitude, phase and/or coherence from said control sounds to SSVEP amplitude, phase and/or coherence from said test sounds in order to determine whether the participant recognises the sound if there is a predetermined change in SSVEP amplitude, phase and/or coherence associated with that test sound.

The invention also provides apparatus for determining if a participant has an interest in the subject matter, the apparatus including: means for presenting to the participant audio visual material including neutral subject matter and particular subject matter; detecting means for detecting brain response signals from the participant during presentation of said audio visual material; calculating means for calculating SSVEP amplitude, phase and/or coherence from said brain response signals; and comparing means for comparing SSVEP amplitude, phase and/or coherence from said neutral subject matter to SSVEP amplitude, phase and/or coherence from said particular subject matter in order to determine if the participant has an interest in the particular subject matter if there is a change in SSVEP amplitude phase and/or coherence associated with the particular subject matter.

The changes in SSVEP amplitude, phase and/or coherence can be an increase or decrease. Also, the magnitude of the change may vary from case to case. One way of determining whether there has been a significant change in SSVEP amplitude, phase and/or coherence is by reference to statistical analyses where a change is regarded as significant at the p<0.05 level where p represents the probability of a Type 1 statistical error (i.e. wrongly rejecting the null hypothesis). Statistical significance can be tested using a number of methods including student's t-test, Hotellig's T2 and the multivariate permutation test. For a discussion of these methods used to analyse the SSVEP see Silberstein R.B., Danieli F., Nunez P.L. (2003) Frontoparietal evoked potential synchronisation is increased during mental rotation. Neuroreport, 14:67-71, Silberstein R.B., Farrow M.A., Levy F., Pipingas A., Hay D.A., Jarman F.C. (1998). Functional brain electrical; activity mapping in boys with attention deficit hyperactivity disorder. Archives of General Psychiatry 1998; 55:1105-12.

The invention will now be further described with reference to the accompanying drawings, in which: FIGURE 1 is a schematic diagram of a system of the invention;

FIGURE 2 is a schematic view of part of the system; and

FIGURE 3 is a schematic view showing in more detail the manner in which visual flicker signals are presented to a participant.

Figure 1 schematically illustrates a system 20 for determining the response of a participant 10 to audio visual material which can be presented to the participant 10 on a video screen 1 and loudspeaker 15. The system includes a computer 6 which controls various parts of the hardware and also performs computation on signals derived from the brain activity of the participant 10, as will be described below. The computer 6 may also store images and/or sounds which can be presented to the participant 10 on the screen 1 or through the loudspeaker 15. The system may include a microphone 3 which is coupled to the computer 6 via a microphone interface 4 so that an operator 2 can address questions to the participant 10. The system may also include a video screen 5 on which can be presented to the operator 2 material relevant to the participant 10 and/or part or all of the material which is presented to the participant 10. The operator 2 may be in an environment where he is able to hear sounds produced by the loudspeaker 15. If, however, the operator 2 was physically isolated from the participant 10, such as by a glass screen or the like, then a separate loudspeaker (not shown) could be provided for the operator 2.

The participant 10 to be tested is fitted with a helmet 11 which includes a plurality of electrodes for obtaining brain electrical activity from various sights on the scalp of the participant 10. The helmet includes a visor 12 which includes half silvered mirrors 17 and

18 and LED arrays 19 and 21, as shown in Figure 2. The half silvered mirrors are arranged to direct light from the LED arrays 19 and 21 towards the eyes of the participant. The

LED arrays 19 and 21 are controlled so that the light intensity therefrom varies sinusoidally under the control of control circuitry 9. The control circuitry 9 includes a waveform generator for generating the sinusoidal signal. The circuitry 9 also includes amplifiers, filters, analogue to digital converters and a USB interface for coupling the various electrode signals into the computer 6.

The system also includes a microphone 13 for recording voice signals from the participant 10. The microphone 13 is coupled to the computer 6 via a microphone interface circuit 14. The system also includes a switch 8 which can be manually operated by the participant 10 in response to certain questions or audio visual displays. The switch 8 is coupled to the computer 6 via a switch interface circuit 7.

The computer 6 includes software which calculates SSVEP amplitude, phase and/or coherence from each of the electrodes in the helmet 11.

Details of the hardware and software required for generating SSVEP 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 participant 10 views the video screen 1 through the special visor 12 which delivers a continuous background flicker to the peripheral vision. The frequency of the background flicker is typically 13Hz but may be selected to be between 3Hz and 50Hz. Brain electrical activity will be recorded using specialised electronic hardware that filters and amplifies the signal, digitises it in the circuit 9 where it is then transferred to the computer 6 for storage and analysis. SSPT is used to ascertain regional brain activity at the scalp sites using SSPT analysis software. For a description of the SSPT technique see Silberstein R.B. (1995) Steady state visually evoked potentials, brain resonances and cognitive processes. In P.L. Nunez, Neocortical dynamics and human EEG rhythms, Oxford University Press, New York 1995, pp 272-303 and Silberstein R.B., Danieli F., Nunez P.L. (2003) Fronto-parietal evoked potential synchronization is increased during mental rotation, Neuroreport 14:67-71.

The psychological response of the participant under investigation and/or the truthfulness of the response will be determined by changes in SSVEP amplitude, SSVEP phase and SSVEP coherence at specific scalp sites. These sites include but are not restricted to prefrontal areas. In addition, activity in deeper regions of the brain, such as the anterior cingulate cortex will also be used.

Verbal questions presented by the operator 2 and the verbal responses by the participant will be picked up via microphones 3 and 13 respectively. The audio signals will be appropriately amplified, filtered and digitised via interfaces 4 and 14 and stored as sound files on the computer 6. This enables the timing of the onset of questions and verbal responses to be determined within an accuracy of 10 microseconds. Alternatively, the participant under investigation may respond to questions via a motor response such as a button push via a microswitch 8 that is interfaced with the computer 6 via interface circuit 9.

The system 20 can be used for a variety of purposes. In one application it can be used to determine whether or not verbal responses from the participant 10 to verbal questions posed by the operator 2 are true or are likely to be true. In this mode the operator 2 would ask the participant 10 a number of questions including control questions which the participant 10 would be expected to answer truthfully and a number of test questions in which the participant may give an untruthful or deceptive answer. The system will be further described with reference to this application but it is to be understood that essentially the same system can be used in other modes. For instance, the screen 1 and loudspeaker 15 may display audio visual material, or images or sounds which include neutral subject matter which is of no particular interest to the participant 10. The audio visual material images or sounds are also provided with test material which may be of particular significance to the participant 10. Test material may, for instance, include an image or voice of a person, crime scene, stolen object or the like and the system can be used to determine whether the participant 10 recognises the test material or not. In another mode, the system may be used to determine the likelihood of the participant 10 committing or recommitting a criminal offence or act of terrorism. In this case, the screen and loudspeaker may display neutral subject matter as well as subject matter related to the nature of the criminal or terrorist activity in order to determine if there is a different response from the participant 10 to this test material.

In all cases, the precise timing of all events presented to the participant 10 are preferably determined with an accuracy of no less than 10 microseconds.

As mentioned above, the visor 12 includes LED arrays 19 and 21. In one embodiment, the light therefrom is varied sinusoidally. An alternative approach utilises pulse width modulation where the light emitting sources are driven by l-10Khz pulses where the pulse duration is proportional to the brightness of the sight emitting sources. In this embodiment, the control circuitry 9 receives a digital input stream from the computer 6 and outputs pulse width modulated pulses at a frequency of l-10Khz. The time of each positive going zero-crossing from the sinusoidal stimulus waveform is determined to an accuracy of 10 microseconds and stored in computer memory 6.

Brain electrical activity is recorded using multiple electrodes in helmet 11 or another commercially available multi-electrode system such as Electro-cap (ECI Inc., Eaton, Ohio USA). The number of electrodes is normally not less than 16 and normally not more than 256, typically 64.

Brain activity at each of the electrodes is conducted to a signal conditioning system and control circuitry 9. The circuitry 9 includes multistage fixed gain amplification, band pass filtering and sample-and-hold circuitry for each channel. Amplified/filtered brain activity is digitised to 16 bit accuracy at a rate not less than 300Hz and transferred to the computer 6 for storage on hard disk. The timing of each brain electrical sample together with the time of presentation of questions, multimedia segment and participant responses is also registered and stored to an accuracy 10 microseconds.

SSVEP amplitude, phase and coherence

The digitised brain electrical activity (EEG) together with timing of the stimulus zero crossings enables one to calculate the SSVEP from the recorded EEG or from EEG data that has been pre-processed using Independent Components Analysis to remove artefacts and increase the signal to noise ratio. [Bell AJ. and Sejnowski TJ. 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 TJ. Sejnowskik, Independent component analysis of single-trial event- related potential Human Brain Mapping, 14(3):168-85,2001.]

Calculation of SSVEP amplitude and phase for each stimulus cycle. Calculation accomplished used Fourier techniques using equations 1.0 and 1.1 below.

a, = — U f(nT + zΔτ) cosf — (nT + /Δr)|

^b" ⁺ '^•ΔφinfønT' + iΔr))

Equation 1.0 Calculation of SSVEP Fourier components where a_n and b_n are the cosine and sine Fourier coefficients respectively, n represents the nth stimulus cycle, S is the number of samples per stimulus cycle (16), Δτ is the time interval between samples, T is the period of one cycle and f(nT+iΔτ) is the EEG signal (raw or pre-processed using ICA).

SSVEPamplUude = ■Jψl + bfj

SSVEPphase = a tan ( -b*- λ

Equation 1.1

Calculation of SSVEP amplitude and phase where a_n and b_n are the cosine and sine Fourier coefficients respectively. Amplitude and phase components can be calculated using either single cycle Fourier coefficients or coefficients that have been calculated by integrating across multiple cycles.

Two types of coherence functions are calculated from the SSVEP sine and cosine Fourier coefficients while patients undertake the cognitive task. One will be termed the SSVEP Coherence ("SSVEPC") and the other, Event Related SSVEP Coherence ("ER- SSVEPC"). The SSVEPC signifies the mean coherence over the duration of a particular interval while the ER-SSVEPC signifies the SSVEPC as a function of time. If it is necessary to examine brain states that change very slowly with time (i.e. minutes to hours) SSVEPC is most suitable while ER-SSVEPC is most appropriate to examine rapid changes in coherence that may, for example, be associated with a response to a question. ER- SSVEPC is described in detail in Silberstein R.B., Danieli F., Nunez P.L., (2003) Frontoparietal evoked potential synchronization is increased during mental rotation, Neuroreport 14:67-71.

SSVEPC

The SSVEP sine and cosine coefficients can be expressed as complex numbers C_n= (a_n , b_n)

where a_n and b_n have been previously defined.

The nomenclature is generalized to take into account multiple tasks and multiple electrodes.

Cg^n- (^ag,e,n j t⁾g,e,n)

where g= the task number e= the electrode n= the point in time

We define the function

Where C* is the complex conjugate of C.

and

1 g,

The SSVEPC is then given by

And the phase of the SSVEPC is given by

ER-SSVEPC

In ER-SSVEPC, the coherence across trials in a particular task can be calculated. This yields coherence as a function of time. The nomenclature can be generalized to take into account multiple tasks and multiple electrodes.

^g,d,e,n (,ag,d,e,n , t⁾g_;d_je;n}

where g= the task number d= the trial within a particular task, eg a specific response e= the electrode n= the point in time

We define the function

and 1 g,el, el,n — O g,e2,d,n)

The SSVEPC is then given by

And the phase of the SSVEPC is given by

The above equations apply to scalp recorded data as well as brain electrical activity inferred at the cortical surface adjacent to the skull and deeper such as the anterior cingulate cortex. Activity in deeper regions of the brain such as the anterior cingulate or ventro-medial cortex can be determined using a number of available inverse mapping techniques such as BESA, EMSE and LORETA.

During the questioning of the participant 10, the visual flicker is switched on in the visor 12 and brain electrical activity is recorded continuously on the computer 6. In addition, all questions and responses will be recorded and stored on the computer 6 as sound files or labeled events as the case may be.

Some questions and responses will be unrelated to matters under investigation (such as criminal or terrorist activity) (control questions and responses) while others will be related to the matter under investigation (test questions and responses). The questions will be selected so that a participant seeking to give a deceptive response will be required to maintain consistency between their current and previous responses. At the end of the questioning, the SSVEP responses associated with the control and test questions can be calculated and separately averaged into test and control responses. SSVEP amplitude, phase and coherence will be calculated at and between recording sites (as appropriate) for control and test responses.

It has been found that, compared to control responses, deceptive responses will normally be associated with greater SSVEP amplitude and phase lag at prefrontal scalp sites and and anterior cingulate. In addition, there will be significant differences in SSVEP coherence between between test and control responses at pre-frontal, frontal and temporal sites.

In the situation where the participant is passively viewing an audio visual segment,

SSVEP responses recorded while the participant viewed neutral material and material associated with criminal activity will be pooled into two categories. The extent to which the criminally related material influences the participant compared to the neutral material will be one factor give an indication of the likelyhood of the participant re-offending.

It is anticipated that the final results will be available within about one minute of the end the recording procedure.

Many modifications will be apparent to those skilled in the art without departing from the spirit and scope of the invention.

Claims

CLAIMS:

1. A method of detecting an untrue or deceptive response of a participant to a cognitive task, the method including the steps of: presenting to the participant a group of cognitive tasks including control tasks and test tasks; detecting brain response signals from the participant during presentation of said group of cognitive tasks; calculating SSVEP amplitude, phase and/or coherence from said brain response signals; comparing SSVEP amplitude, phase and/or coherence from said controlled tasks to SSVEP amplitude, phase and/or coherence from said test tasks; and determining that the subject is giving an untrue or deceptive response if there is a predetermined change in SSVEP amplitude, phase or coherence associated with the test tasks.

2. A method as claimed in claim 1 wherein the control tasks are control questions to the participant, the answers of which are likely to be answered truthfully by the participant and the test tasks and test questions to the participant which are likely to be answered untruthfully or deceptively by the participant.

3. A method as claimed in claim 1 or 2 wherein the questions are presented orally or in written form to the participant.

4. A method as claimed in claims 1, 2 or 3 including determining whether said predetermined change is statistically significant.

5. A method as claimed in any one of claims 1 to 4 including the step of recording the timing of the cognitive tasks and the timing of the detected brain response signals.

6. A method as claimed in claim 2 wherein the SSVEP amplitude, phase and/or coherence associated with the control questions and test questions are separately averaged into control brain responses and test brain responses.

7. A method as claimed in claim 6 calculating task related changes in SSVEP amplitude, phase and/or coherence in deeper regions of the brain using inverse mapping.

8. A method as claimed in claim 7 wherein the inverse mapping is carried out using BESA, EMSE or LORETA.

9. A method as claimed in claim 6 including the step of determining that an untrue or deceptive answer has or is likely to have been given by a participant if the SSVEP coherence to a test response is greater than the SSVEP coherence to a control response.

10. A method as claimed in claim 8 wherein the SSVEP coherences are obtained from pre-frontal, frontal and/or temporal sites.

11. A method of determining whether a participant recognises a test image, the method including the steps of: presenting to the participant a group of images including control images and test images; detecting brain response signals from the participant during presentation of said group of images; calculating SSVEP amplitude, phase and/or coherence from said brain response signals; comparing SSVEP amplitude, phase and/or coherence from said control images to SSVEP amplitude, phase and/or coherence from said test images; and determining that the participant does recognise the image if there is a predetermined change in SSVEP amplitude, phase and/or coherence associated with the test images.

12. A method as claimed in claim 11 wherein the test images include the image of a person, an image of a crime scene, an image of a stolen object.

13. A method of determining whether a participant recognises a test sound, the method including the steps of: presenting to the participant a group of sounds including control sounds and test sounds; detecting brain response signals from the participant during presentation of said group of sounds; calculating SSVEP amplitude, phase and/or coherence from said brain response signals; comparing SSVEP amplitude, phase and/or coherence from said control sounds to SSVEP amplitude, phase and/or coherence from said test sounds; and determining that the participant does recognise a test sound if there is a predetermined change in SSVEP amplitude, phase and/or coherence associated with that test sound.

14. A method as claimed in claim 13 wherein the test sounds include the voice of a person.

15. A method of determining if a participant has an interest in particular subject matter, the method including the steps of: presenting to the participant audio visual material including neutral subject matter and particular subject matter, detecting brain responses from the participant during presentation of said audio visual material; calculating SSVEP amplitude, phase and/or coherence from said brain response signals; comparing SSVEP amplitude, phase and/or coherence from said neutral subject matter to SSVEP amplitude, phase and/or coherence from said particular subject matter; and determining that the participant does have an interest in the particular subject 2006/000628

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matter if there is a predetermined change in SSVEP amplitude, phase and/or coherence associated with the particular subject matter.

16. A method as claimed in claim 15 wherein the particular subject matter includes audio visual material relating to a person, crime scene, stolen object.

17. A method as claimed in claim 11 or 15 wherein the test images or particular subject matter relate to criminal or terrorist activities.

18. Apparatus for detecting an untrue or deceptive response of a participant to a cognitive task, the apparatus including means for presenting to the participant a group of cognitive tasks including control tasks and test tasks; detecting means for detecting brain response signals from the participant during presentation of said group of cognitive tasks; calculating means for calculating SSVEP amplitude, phase and/or coherence from said brain response signals; comparing means for comparing SSVEP amplitude, phase and/or coherence from said control task to SSVEP amplitude, phase and/or coherence from said test tasks in order to determine if the responses to the test tasks are or are likely to be untrue or deceptive.

19. Apparatus for determining whether a participant recognises a test image, the apparatus including: display means for presenting to a participant a group of images including control images and test images; detecting means for detecting brain response signals from the participant during presentation of the group of images; calculating means for calculating SSVEP amplitude, phase and/or coherence from said brain response signals, comparing means for comparing SSVEP amplitude, phase and/or coherence from said control images to said SSVEP amplitude, phase and/or coherence from said test images in order to determine whether or not the participant does recognise the image if there is a predetermined change in SSVEP amplitude, phase and/or coherence associated with that test image.

20. Apparatus for determining whether a participant recognises a test sound, the apparatus including: a loudspeaker for presenting to the participant a group of sounds including control sounds and test sounds; detecting means for detecting brain response signals from the participant during presentation of said group of sounds; calculating means for detecting SSVEP amplitude, phase and/or coherence from said brain response signals; and comparing means for comparing SSVEP amplitude, phase and/or coherence from said control sounds to SSVEP amplitude, phase and/or coherence from said test sounds in order to determine whether the participant recognises the sound if there is a predetermined change in SSVEP amplitude, phase and/or coherence associated with that test sound.

21. Apparatus for determining if a participant has an interest in the subject matter, the apparatus including: means for presenting to the participant audio visual material including neutral subject matter and particular subject matter; detecting means for detecting brain response signals from the participant during presentation of said audio visual material; calculating means for calculating SSVEP amplitude, phase and/or coherence from said brain response signals; and comparing means for comparing SSVEP amplitude, phase and/or coherence from said neutral subject matter to SSVEP amplitude, phase and/or coherence from said particular subject matter in order to determine if the participant has an interest in the particular subject matter if there is a change in SSVEP amplitude phase and/or coherence associated with the particular subject matter.