The science of speech
Allen Hirson, Senior Lecturer in Phonetics at City, talks about speech and phonetics...
At the CNRU we seek to understand human thought and behaviour, taking a perspective that is closely informed by the properties of neural activity in the brain.
We bring this distinct biopsychological perspective to topics traditionally investigated by cognitive and social psychologists, for example perception (vision, audition, touch and temporal perception), attention (both within and across sensory modalities), memory and interpersonal social processes (including face and body perception, imitation, "mirror" neurones and action understanding). Cognitive neuroscience forms an important part of the MSc in Cognitive, Social and Clinical Neuroscience and the BSc in Psychology. It informs teaching right across the three years of the BSc degree including final-year option modules on "Topics in Cognitive Neuroscience", "Social Perception" and "Disorders of the Mind" which are part of the BSc in Psychology with Cognitive and Clinical Neuroscience pathway.
Dr Beatriz Calvo-Merino
Location: Department of Psychology, Rhind Building - Level 4, Room D401/402 Tel: +44 (0)20 7040 4211. EEG lab2 is located on the ground floor in room DG08A.
The EEG labs are purpose-built units in the Department of Psychology. EEG enables the measuring of electrical brain activity occurring during all kinds of externally and internally triggered cognitive processes such as sensory perception, selective attention, action preparation, executive control processes, learning, working memory, etc. We employ a 64- / 32-channel EEG setup and all recordings are performed in an acoustically and electrically shielded chamber.
Groups of neurons firing synchronously create electrical potentials that can be measured by electrodes placed on the scalp. When the electrical signals from a given electrode are graphed over a period of time, the resulting representation is called an EEG (electroencephalogram). The EEG ultimately provides information about the time course and location of the neural firing, allowing researchers to draw conclusions about the underlying brain activity and its relation to cognitive functions.
The image below shows EEG traces from commonly used electrodes, all placed on the scalp. Although such information is the basis of the conclusions researchers in the lab make about brain function, a fair amount of analysis must be performed before many interesting conclusions can be made. Very little can be concluded by simply looking at these traces, as one can usually only see noise not related to brain activity (e.g. eye blinks), or alpha waves when a person becomes very sleepy!
In order to record the electrical signals indicating brain activity, participants must wear a cap with embedded electrodes. The person above is modeling one such cap, and sometimes participants also wear facial electrodes in order to record eye movements, as such movements affect the readings from the electrodes monitoring brain activity. The facial electrodes and the electrodes in the cap must be filled with a conductive gel (a saline solution that easily washes off skin and out of hair) in order to obtain good electrical signals.
An experiment consists of a participant repeatedly performing a specific cognitive task while one of the lab's computers records the electrical signals from the electrodes. During the experiment, the signals from the electrodes are relayed through the amplifiers to the computer via the wires and connectors that are visible in the back of the head of the participant on the photo.
Since just looking at the raw EEG data does not relay much useful information to the researcher, they must be mathematically transformed in order to answer the questions a given study has posed. The most frequent analysis technique is to average the EEG recordings across multiple trials, where a trial is defined in relation to some event such as a subject response or the appearance of a visual stimulus. Such averaging reduces the effects of electrical signals not related to the brain activity evoked by the event in question. The waveform produced after averaging across trials is called an event related potential (ERP). Below is an example of averaged ERPs in response to tactile stimuli applied to one of the hands recorded over ipsilateral (same side as tactile stimulation) and contralateral (opposite side as tactile stimulation) somatosensory cortex.
Are you interested in participating in an EEG study? The following description will give you an idea of a typical EEG study in our lab. Please, read this information before participating in a study.
Basically you will be sitting in front of a computer screen doing a simple task. For example: On the screen you see a circle flashing in different colours, every time the triangle turns green you press a button (this is a very basic example). In most of our experiments we measure changes in your brain's activity while you are performing the task - that is we measure your electroencephalogram (EEG). In order for us to do this, you need to wear a cap with electrodes on your head during the experiment. We use the same equipment to do this as is used in hospitals for monitoring patients.
On average an experiment takes about 2 to 3 hours. About half an hour is needed to put the cap on and ensure that a good measurement is possible. Also, you will want to wash your hair afterwards, to remove the left-behind bits of conductive gel from your hair. We have a hand-held shower, clean towels, hair-care products etc. for you to use.
We pay each participant £7 per hour in cash (or £20 for a 2.5 - 3 hour session). We do not pay for your travelling expenses.
We are looking for healthy people between the age of 18 and 45. The experiments take place in a small cabin and for this reason it is not wise to take part in an experiment if you are claustrophobic. It is important to be fit and well-rested when you take part in an EEG experiment. Also, it helps if you do not use any hair-care products like conditioner, oils or wax in your hair. Finally, if you are wearing contact lenses but also have a pair of spectacles you could wear, it is advisable to bring your spectacles, because some participants complain of dry eyes when they are doing our experiments.
The electrodes we use to record the EEG are fitted in a cap, which looks like a bathing cap with a lot of wires coming out. To make a good contact between the skin and the electrodes we clean the skin underneath the electrodes with some alcohol and then fill the electrode with a conductive paste (this is a completely harmless saline solution). Some of this paste will be left behind in your hair after we take the cap off, so you will probably want to wash your hair afterwards and we have all the necessary facilities in our lab.
Location: Department of Psychology, Rhind Building - Level 5, Room D512 Tel: +44 (0)20 7040 4561.
Transcranial magnetic stimulation, or TMS, is a relatively recent technique for stimulating the outer layer of the brain, particularly the cerebral cortex. Brain cells, known as neurones, pass messages by generating spikes of electrical activity, known as action potentials. In TMS, a rapidly changing magnetic field is induced in a hand-held coil in order to electrically activate the neurones in a small area of cortex located under the coil.
Broadly speaking, TMS comes in three varieties. In single-pulse TMS, stimulation is delivered once every few seconds. In paired-pulse TMS, two TMS pulses are fired very close together in time to see how they interact. Finally, in repetitive TMS or rTMS, a train of pulses are delivered at a rate varying from once per second to 50 or even 100 times per second.
TMS is used for both clinical and research purposes. Clinically, TMS can be used as a diagnostic tool to assess whether the nervous system is working properly. TMS is applied to the part of the brain that sends commands to the muscles of the body (the primary motor cortex) and the speed with which a muscular response occurs is measured. TMS has also been used to treat conditions such as depression. Research investigating the usefulness of TMS for treating neurological and psychiatric conditions is ongoing, but please note that we do not run clinical trials or provide TMS as a therapy/treatment at City.
In cognitive neuroscience research, TMS is used to determine how the brain controls our behaviour. Paired-pulse TMS is used to figure out the ways in which different parts of the brain are connected together. Single-pulse TMS is used to activate muscles of the body and assess the state of the motor system in different experimental conditions. Finally, both single-pulse and repetitive TMS can be used to briefly interfere with the activity of a small area of the brain, so we can see how behaviour is affected. By temporarily turning off a small part of the brain, this approach yields insights that are similar to those obtained by neuropsychologists, who study patients with lesions (damage) to particular areas. Hence TMS is sometimes described as a "virtual lesion" technique.
TMS feels a little like being tapped on the head. Most people don't really notice it after the first few pulses. However, because TMS can activate muscles on the scalp, it is sometimes experienced as being uncomfortable. In these cases, it may give rise to a short-lived headache. Our participants are encouraged to tell us immediately if they don't feel comfortable.
TMS has a good safety record, and is not believed to have any long-term health effects. The biggest concern for most participants is that at high intensities and high stimulation rates there is a possibility of inducing a seizure akin to those experienced by epileptic patients. There are published safety guidelines about what levels of stimulation are safe, and we adhere to these guidelines closely. We discuss the risks associated with TMS with our participants, and we ask a series of questions to make sure that these risks are not elevated for them.
TMS is generally safe, but there are some people who should never have TMS, and there are some people who should only have it in special cases where there is a potential benefit for them, like a clinical trial. We will generally not test you if:
*You have a pacemaker, or any other electronic device inserted in your body
*You have any kind of neurological history, for example a stroke or a serious head injury
*You have epilepsy, or a family history of epilepsy
*You are currently taking prescription medication (with the exception of the contraceptive pill)
*You are pregnant.
In a typical experiment, you will be seated in front of a computer doing a straightforward (but sometimes challenging) task. Examples include reacting as fast as possible to lights or sounds, or making judgements about things like whether a weak light has been presented, or how long it was presented for. Before you begin the task, we will apply some pulses of TMS to work out the right strength and location of stimulation for you. During the task, we will apply TMS from time to time to see how it affects your performance.
Experiments may last anywhere from one to three hours. You will have opportunities to take breaks, and you will be paid for your participation at a rate of around £7.50 per hour. We are happy to talk about the purpose of the experiment, although we may withhold some details until afterwards to keep you "naïve". Unfortunately, we cannot pay transport costs.
If you would like to participate in a TMS experiment or have any queries regarding participation, please send an email to Dr Kielan Yarrow or the CNRU lab.
Location: Department of Psychology, Rhind Building - Level 4, Room D403 Tel: +44 (0)20 7040 4211.
Eye tracking provides an objective and quantitative measure of a person's point of gaze in a visual scene displayed e.g on a computer screen. Recording and subsequently analysing even tiniest eye movements when participants perform experimental tasks with varying sensory, motor or cognitive demands prove very revealing with respect to many cognitive and attentional processes investigated in cognitive neuroscience. Eye tracking devices such as the one we are using in our lab collect up to 360 gaze data points per second and therefore allow comprehensive analyses of eye movement characteristics such as fixation time and frequency, length and direction of saccades as a direct function of the experimental task.
There are different types of eye tracking devices. The one we are using in our lab is a model where all crucial optic components for eye tracking are mounted to a chinrest: An eye camera that captures the features of the eye gaze tracking is based on, an illuminator that allows a good discrimination of the pupil by means of an infra-red beam and a small sense camera that records the visual display that is to be viewed. A small mirror also attached to the chinrest fulfils an important function: Properly positioned slightly below the eye, it allows having the eye camera and the illuminator mounted above the eye (instead of in front of the eye where these components would be in the way).
Eye tracking takes advantage of the distinct light-reflective properties of two features of the eye: The pupil and the cornea. On its way to the retina, light passes the cornea, a transparent layer that covers the front of the eye, and enters the eye through the pupil, a small translucent opening in the otherwise optically opaque iris. Traversing the gelantinous liquid filling in the inner part of the eye, it eventually reaches the photo-sensitive receptor cells in the retina where the incoming light is converted into neural signals.
The retina at the back of the eye usually reflects a portion of the incoming light back to its source along the very same path the light initially came in. Usually, bright pupil technique the pupil nevertheless appears dark because the location the eye is observed from rarely ever coincides with the location of the light source.
Eye tracking, however, takes advantage of this reflective phenomenon with a careful alignment of the optic components: The illuminator projects a harmless beam of infra-red light into the eye on a path that is coaxial with the imaging direction of the eye camera. Due to the retinal reflection of this light beam, the otherwise dark pupil subsequently appears bright to the eye camera. This allows a robust and reliable discrimination of the pupil from the rest of the eye.
Proper tracking of a person's point of gaze, however, requires the extraction of a second feature of the eye. Once again, it is the infra-red beam from the illuminator that comes into play here: although the cornea is the overall translucent, a small portion of the light beam is nevertheless reflected from it. This corneal reflection (CR) appears as a very small, very bright dot somewhere on the eye image. Ideally, the brightness of the illuminator is adjusted in a way that the pupil can clearly be distinguished from the darker background and the CR from the pupil.
The illuminated pupil is considered the "center" of the eye and shifts whenever the eye moves. The corneal reflection, however, remains in the same location and is therefore used as an anchor point for the head position with respect to the camera. For each eye picture the camera captures during eye tracking, both the pupil and the CR are identified and the angle of the eye with respect to the visual stimuli is computed from these two elements.
To ensure that eye position and gaze direction are the same, it is crucial that the participant's head position does not vary during stimulus presentation. To this end, participants are asked to put their head into a chinrest. After finding a comfortable seated position with the head in the chinrest, the small mirror attached to the chinrest is positioned so the eye camera captures a complete and sharp close up image of the participants left eye and the illuminator is adjusted in a way that allows an optimal discrimination between the pupil, the CR and the rest of the eye.
Before starting the actual experiment, the eye tracking system also needs to be calibrated. The calibration procedure accounts for individual differences in eye anatomy and consists of collecting point of gaze data for a set of predefined target points in a stationary visual display. Participants are simply asked to look at various target points while the respective eye data get stored in the system. An accurate calibration of the system for each individual participant is crucial for obtaining valid eye movement data.
Our members have experience with a wide range of neuroscientific techniques, including neuropsychological testing, psychophysics and fMRI. We have particular strengths in the use of EEG, TMS and Transcranial Electric Stimulation (a weak current applied to the scalp), in addition to measures of human behaviour (e.g. response times, response errors, and eye movements) and physiological measures (e.g. galvanic skin response and heart rate). We test neurologically normal individuals, special populations (e.g. people with synesthesia) and people with expertise or acquired skills (e.g. dancers, musicians, athletes), as well as people with brain damage (e.g. neglect or split-brain patients), psychiatric diagnoses (e.g. schizophrenia), sensory deficits (e.g. visual and hearing impairments) or other disorders (e.g. dyslexia or autism).
We regularly run behavioural, EEG and TMS studies. If you are interested in taking part in our studies or have any queries regarding our research, please email the CNRU lab (see address below).
Please state in the subject title of your email whether you would like to participate in a behavioural, EEG or TMS experiment, or state ANY if you are interested in taking part in any of the experiments regardless of research method.
To participate, email: email@example.com
Allen Hirson, Senior Lecturer in Phonetics at City, talks about speech and phonetics...