Measuring N170 Potential using Gaming EEG System

Functional specialisation of inferotemporal cortex

· Neurons in the ventral stream exhibit response properties that are important for object recognition such as selectivity for shape, colour and texture

· Some neurons (such as those in IT cortex) exhibit even greater selectivity, respond preferentially to faces or objects

 

Event-related potentials (ERPs) -Embedded within the EEG

· Event-related potentials refer to electrical potentials that are associated with specific events (e.g. Stimulus on a computer screen or a motor movement)

· Individual EEG recordings are highly variable or noisy

· By averaging brain activity across multiple presentations of the same/similar events, we end up with a highly replicable waveform

· Trial averaged ERP waveforms consist of a sequences of positive and negative voltage deflections, which are called ERP peaks or components

 

Emotiv EPOC+, Moving from EEG to ERPS

· To average the EEG signal, we need to know when in out EEG recording a stimulus was presented

· To do this, we use an event-marking system comprised of; Audio cable (1),Blue power cable (2), Transmitter unit (3), Receiver unit (4)

· How it works: When a stimulus is presented, the transmitter unit transmits an infrared signal to the receiver unit on headset. The receiver unit sends a pulse to 2electrodes,which is recorded in EEG

 

The experiment - Testing functional specialisation in visual cortex

· The N170 is a "face-sensitive" ERP (negative peak) that occurs around 170 ms after stimulus onset over occipito-temporal brain regions

· N170 is larger in response to faces than to other objects, but it is also sensitive to face inversion, which significantly delays N170 onset

 

Task:

Is the stimulus presented upright or inverted

Experimental design

Depend - What we measure

· Reaction time

· The difference between the slides

· Faces - big peak

· Other slide - small peak

Independent - What varies

· The picture (Stimulus)

· Inversion

Hypothesis - Always find evidence against null hypothesis

· H0 (null hypothesis): N170 response to faces and objects is the same

· H1 (alt hypothesis): N170 response to faces is larger than the N170 response to objects

· H0 (null hypothesis): N170 response to upright and inverted faces is the same

· H2 (alt hypothesis): N170 response to inverted faces is slower than the N170 response to upright faces

Conditions

· 4 conditions each 75 images. Total images = 4 x 75 = 300

Set- up for lab session

· Place headset on the head

· Reference electrodes on the mastoid (=bone behind the ear)

· Frontal electrodes on the hairline

· Back of the headset should be horizontal

· Soak dental roll in saline solution

· Place dental rolls in mastoid electrodes

· Place dental rolls in active electrodes

· Adjust dental rolls and electrodes until impedance is acceptable

· Good impedance = green dot in contact quality screen in Test Bench

Lab report

· Normal research paper

· Sub-heading

· Full sentencing

· Should be able to replicate

· Lab report helps you develop skills to communicate scientific information in a clear and concise manner

Introduction

· A brief background to explain your hypothesis and how you want to test it

Method

· The stimuli, procedure and analysis with much details that the experiment can be duplicated

Results

· Two figures

· No interpretation

· Put labels

· Describe what you can see

· Simply explain the data with no interpretation - The peak, time

· Raw signal is too small

Discussion

· Summarise what was found

· Go back to introduction and hypothesis

· Interpretation of data to support or negate the hypothesis

· Explain the limitations of the study and discuss future direction

Reference

· APA Referencing Style is an author- date citation style. It has two main features

· In-text citation: when you refer to another author's work you must cite your source by providing the last name(s) of the author(s) and the year of publication

· E.g. (Bentin et al., 1996)

· The reference list: appears at the end of your assignment and includes a full description of each source you have cited, listing them in alphabetical order by the author's last name

· Bentin, S., Allison, T., Puce, A., Perez, E., & McCarthy, G. (1996). Electrophysiological studies of face perception in humans. Journal of cognitive neuroscience, 8(6), 551-565

· Make sure you reference other people's work and do NOT use direct quotes

 

FACE PERCEPTION

Central visual pathways

· Processed in occipital

· Ventral pathway - recognise what object

· Dorsal pathway- Where/ spatial pathways

· Neurons in the ventral stream exhibit response properties that are important for object recognition such as selectivity for shape, colour and texture

· Some neurons (such as those in IT cortex) exhibit even greater selectivity, respond preferentially to faces or objects

Face perceptions

· Faces are the one of most salient visual stimuli to humans

· Face perception and recognition are high cognitive functions that mature very early in life

 

Introduction - Previous empirical evidence

· Is there any neural region specialised for processing faces?

· Single cell recordings show that inferotemporal cortex activates to faces not other stimuli

· Deficit in recognition of faces - Prosopagnosia - occur after the lesion to the inferior occipitotemporal lobe

· PET and fMRI studies show right dominant activation in the inferior occipitotemporal lobe during face recognition compared with other stimuli

NOTE: You should have references in your LAB REPORT if stating the above

 

What is ERP

· Event-related potentials refer to electrical potentials that are associated with specific events (e.g. a stimulus on a computer screen or a motor movement)

· Individual EEG recordings are highly variable or noisy

· By averaging brain activity across multiple presentations of the same/similar events, we end up with a highly replicable waveform

· Trial-averaged ERP waveforms consist of a sequence of positive and negative voltage deflections, which are called ERP peaks

What is N170 - Why did we run this experiment?

 

 

Hypotheses (Introduction)

1. Hypothesis 1

· What we know:

· N170 is larger in response to faces than to other objects

· What we test:

· H0 (null hypothesis): N170 response to faces and objects is the same

· H1 (alt hypothesis): N170 response to faces is larger than N170 response to objects

1. Hypothesis 2

· What we know

· N170 is sensitive to face inversion, which delays N170 onset

· What we test:

· H0 (null hypothesis): N170 response to upright and inverted faces is the same

· H1 (alt hypothesis): N170 response to inverted faces is slower than the N170 response to upright faces

· Selected P8

· Data was pre-processed = average waveform

· 14 participants

· First hypothesis - first graph

Variables

· Independent

· Manipulation of stimuli

· The slides

 

· Dependent

· Data

· N170 size (=amplitude)

· N170 time (=latency)

Method

· Event marking system was added to the commercial Gaming Emotiv Epoc

· The electrodes on Mastoid bones were considered as Reference electrodes

· Stimuli were presented on desktop

· 4 conditions each 75 images

· Total = 4x75=300

· In 3 blocks

Task

· Is the stimulus presented upright or upside down?

· 75 trials per condition

Where do you look for N170?

· The N170 is a "face sensitive" ERP (negative peak) that occurs around 170 ms after stimulus onset over occipito- temporal brain regions

Data pre-processing

· Artefact rejection

· Filtering

· Averaging

Results

Discussion

· We found bigger N170 for faces compared with watches that supports our hypothesis

· Can stimulus complexity account for this?

· Can stimulus shape account for this?

· Can stimulus colour account for this?

· Can the task account for this?

· N170 is also delayed for inverted faces that supports our hypothesis

· Face recognition versus face processing

· Specific/ general limitations?

· Future directions?

Lab report: General point

· Write from the perspective of the researcher

· No bullet points

· Read a few articles to get the general format

· Scientific language

· No jargon

· Choose you words carefully

Introduction

· Introductory sentence

· State H0 and H1

· State what the dependent and independent variables are

Methods

· Past tense

· Useful things are the ones needed to replicate your study

· What EEG system did you use?

· How many trials did you do?

· What were the stimuli, how were they presented , for how long?

· What electrode are you analysing?

· Useless things are the one specific to your study, that other researchers won't are about

· We picked someone from our group to wear headset

· The rest of the group looked at the software

Results

· The graphs are labelled

· Axes labels

· Graph legend

· Title

· Electrode

· Figure description would be nice

· Explain how the results relate to the hypotheses

Discussion

· Re-state the aim and your main result

· Then conclude on what the ERP component reflects

· Integrate your results in the context of the previous literature:

· Why is your study important?

· What does it show that hasn't been showed before

· What has already been done about this (in humans/animals/ with other techniques)

· Are the evidence covering to a solution, or is each technique showing different things?

· Why is the process that you studies important?

· This paragraph should be based on previous literature and should be interesting

· Limitation: focus on one good point instead of many, explain how this actually influences your interpretation/ the date

· Is there anything in the design that limits how far you can go with the interpretation?

· Does the technique itself limit how far you can go with interpretation