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Eye blinks and Eye Movements in Cognition
Lab Protocol
Eye Blinks and Eye Movements in Cognition[1]
Psych 130—by Howard Thorsheim
Introduction
Eye blinks and eye movements are behaviors. They both provide you the researcher with information about what a participant is paying attention to. More than artifacts of the human neuro-muscular system, current theory and empirical research suggest a key role in cognition for both eye blinking and eye movement. Both are involved in significant ways in the processing of information by the brain. At issue is how they play a role in providing information for cognition.
Eye Blinks
The first behavior studied in today’s lab is the eye blink response achieved through the contraction of sets of muscles (See Figure 3). Orchard & Stern (1991) identify three types of eye blinks: (a) reflex blinks (in response to something invading the eye), (b) voluntary blinks (as a result of a decision to blink), and (c) endogenous blinks (due to perception and information processing). These eye blinks are the focus of interesting psychological research.
Reflex blinks are instinctive responses that guard the eyes against eye blinks and dust; they are also part of the startle response to loud noises. The blink reflex can be classically conditioned to a neutral stimulus such as a tone. After several pairings of a tone and eye blink, the tone itself will generate the blink. This can be demonstrated easily in class using an eye blink.
Voluntary blinks are under conscious control and include squinting and winking. Applications of voluntary blinking include their use as control signals for communicating when diseases have made other forms of communication difficult or impossible (such as AIDS, Multiple Sclerosis, Muscular Dystrophy, or Alzheimer's).
Endogenous (meaning "originating from or due to internal causes") blinks occur during reading or speaking and reflect changes of attention and changes in thought processes. The more attention required by a task, the fewer endogenous blinks occur.
The typical duration of eye closure during blinks is 40 to 200 milliseconds (msec.). Useful and important information for distinguishing among the various forms of eye blinks is provided by the fact that their shapes (“pulse envelopes”) reliably differ in both duration and amplitude. The pulse envelope is the outer border of the pulse (See Figure 1).
Summary
Amplitude Type of Blink
Highest: Startle blinks
Next highest: Voluntary blinks
Lowest: Endogenous blinks
Duration Type of Blink
Short: Endogenous blinks
Medium: Startle blinks
Long: Voluntary blinks
Figure 1. Eye blink amplitudes and durations
An interesting research issue that you could investigate is the specific instant at which blinks occur during visual attention. Research is quite clear that blinks do not occur randomly during reading. Thus, an important and useful question of interest relates to when eye blinks occur depending on what one is reading (e.g., content, difficulty, etc.).
Figure 2. Actual Electrooculogram (EOG) for eye blinks. . 2. Actual analog EOG for eye blinks ;. 2. Actual analog EOG for eye blinks ;Sample contains voluntary, endogenous and startle eye blinks.
Eye Movements
The second behavior studied in today’s lab is eye movement (side to side, and up and down). The fact that both eyes move and work together is a remarkable achievement, particularly since the two eyes are not connected mechanically in any way! This is in great contrast to the eyes of a toy doll. The doll's eyes are wired together and, thus, move up and down together.
Eye movements are controlled by the brain in conjunction with cranial nerves and eye muscles. The eye muscles attached to the exterior of the eyeball are called extra-ocular muscles (extra in extra-oculor it means “outside of the eye”). There are three pairs of extra-ocular muscles that work together to control each eyeball, and the two eyeballs together operate in tandem.
Eye movements are produced by extra-ocular muscles that contract, pulling the eye first one way and then another way. Figure 3 shows these muscles.
Figure 3. Muscles of the right eye (Williams, Warwick, Dyson, & Bannister (Eds.), (1989).
The superior rectus (superior means above the eye) and inferior rectus (inferior means below the eye) are extra-ocular muscles that control the up-and-down movement of the eye. The lateral (on the same side as an ear) rectus and medial (on the side closest to the nose) rectus control side-to-side movement. The superior and inferior oblique muscles control the rolling of the eyes.
Efficient readers move their eyes in a rather complex way; they do not simply move their eyes at a constant speed across the page. Horizontal (back and forth) or vertical (up and down) movements of the eye that occur when looking out at the world--or when reading are called Saccades (pronounced sah-kades’). For example, when readers move their eyes from one point of fixation on a page to the next, these movements are called forward saccades. Movement back to reread a word or longer selection on the same line is known as a regressive saccade (to regress is to go back). A variation of the regressive saccade is when a person sweeps his or her eyes back to begin reading the next line. This is called a sweep to beginning of the next line. When readers stop because they wish to pay attention to a certain portion of the text, this is called a fixation pause. These saccadic (pronounced sah-cad'-ick) movements and eye pauses can be used to measure many kinds of interesting cognitive processing. This is another possible measurement tool to explore in lab.
Figure 4. Terms for eye movement during reading
The measurement of eyeball movement during reading and the visual tracking of a target is called electrooculography (EOG). These EOG signals are created by the fact that the rear (posterior) of the eyeball is negative relative to the front (anterior) of the eyeball, setting up a dipole, as shown in Figure 5.
Figure 5. Dipoles that generate the electro-oculogram Dipoles which generate the Electrooculogram;. 10 Dipoles which generate the Electro-oculogram;
Figure 6. Stylized sketch of typical eye movements during reading three lines of text.
Figure 6 , illustrates how eye movements would be depicted on the electrooculogram (EOG) when reading three consecutive lines of text. See if you can identify the other unlabeled parts of the EOG (e.g., fixation points, and saccades).
Figure 7 shows how to place electrodes above and below the eye to provide information about up and down movement of the eyeball, in addition to eye blink information. (NOTE: In Figure 7 one electrode is misplaced. Can you tell which one, and where it should be placed? You will need to in order to collect accurate data.)
Figure 7. Electrode Placement
Figure 7 also shows how electrodes placed on the right and left external canthi of the eyes (i.e., the outside or lateral location, just next to each eye) will pick up the change in left and right orientation of the +/- dipole of each eye. These electrodes will provide information about saccades, line changes, and fixation points.
For investigating a number of interesting psychological questions, the EOG may be used as a general research tool to measure direction of gaze, as well as the length of fixation. In combination, the electrodes provide information about where the eyeball is oriented (direction of gaze) in an X-Y Cartesian coordinate system, as well as about eye blinks. Electrodes on the sides of the eyes provide information about lateral movement (X-axis) and electrodes placed above and below the eyes provide information about up and down movement (Y-axis) and eye blinks.
The typical kind of response one finds is illustrated in Figure 8.
Figure 8. Typical EOG recordings during casual eye movements
Eye blinks and Eye Movements--Working Together
Certain kinds of eye blinks may occur at times when a reader does not need to be taking in information, for example, when moving from one point of fixation to the next (a forward saccade or a regressive saccade), at sweep to the beginning of the next line changes, or when moving back to reread a selection on the same line (regressive saccades). Try to notice in lab if these movements inhibit certain kinds of blinking when the reader needs to pay attention, such as during fixation pauses. On the other hand, other kinds of eye blinks may occur because they are associated with various kinds of cognitive processing.
Objectives
• To investigate the relationship between eye behavior and attention (specifically, eye blinks and eye movement).
• To investigate eye blinks and eye movements, using sophisticated instrumentation
• To investigate the relationship between types of eye blinks and eye movements, and the time at which they occur during the reading various kinds of material that you have brought to lab.
• To suggest ideas for your Create Your Own Lab project.
Terms
8
Eye blinks and Eye Movements in Cognition
Canthus (plural = canthi)
Dipole
Electrode
Electro-oculogram
Endogenous
(EOG)
Extra-ocular
Fixation point
Frequency
Inferior (below)
Lateral vs. Medial
Line change
Rectus Inferior
Rectus Lateral
Rectus Medial
Rectus Superior
Reflex
Saccades
Saccadic
Superior
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Eye blinks and Eye Movements in Cognition
Method
Teams
You will work in three-person groups. Researcher A will be the source of data (the Participant). Researcher B will be engaged in running the BIOPAC and recording observations. Researcher C will present stimuli, and make notes of what is being done. Then roles will be switched. A will be B, B will be C, and C will be A. Do this until all members have been the Participant. All three members of the triad will share their other observations, notes, and data with each other to inform their lab notes. The eye blink data from the EASY TEXT HARD TEXT task will be pooled from all triads.
Apparatus and Materials
BIOPAC Workstation
Alcohol-acetone Prep Pads
Non-latex gloves
Printed copies of text material to be read that you brought to lab.
BioPac Lesson 10 EOG 1
BioPac Electrode Lead Set (SS2L) (you will use two sets)
Disposable Electrodes (you will use 6 per person)
Remember to put on a lab coat.
Activity I: Data Collection
Note that underlined items are suggestions that you make observations that you should record in your lab notebook. Your lab notebook should also include any deviations or revisions you make in procedure or other observations you make about the materials, procedure, or data.
Objective
You will explore eye movements and eye blinks while reading a selection you brought to lab (this could also include things in other languages, sheet music to sight read, etc.). IN the protocol below, this is referred to as the exploratory material. In addition, you will use the information from the workstation to calculate your results. Before you start making recordings, coordinate with your team what you are going to be looking for.
Procedure
1. Make sure BioPac MP30 unit is OFF, that is, no green lights are on, in the front of the MP30 box.
2. Plug in the electrode leads (SS2L) into the MP30. Horizontal is in channel 1 and vertical is in channel 2.
3. Turn on MP30 using the switch at the rear of the box.
4. Always wear non-latex gloves when working with participant
5. Clean the skin with alcohol pads where the electrodes will be placed. Important: make sure you squeeze out 3 drops of alcohol from the prep pads before using them to prevent alcohol running into Participant’s eyes!!
Figure 10. Shows Experimenter cleaning one of the electrode locations.
Important to note: For accurate recordings, attach the electrodes so they are horizontally and vertically aligned
Figure 11. The typical placement of Electro-oculogram (EOG) electrodes for BioPac Lab 10. (NOTE: One electrode is misplaced in the picture above to test you. Can you tell which one, and where it should be placed? You will need to identify it, in order to collect accurate data.)
6. Attach the horizontal electrode lead set (SS2l) from channel 1 to electrodes
7. Attach the vertical electrode lead set (SS2L) from channel 2 to electrodes.
Table 2: Important Instructions for where to connect each color electrode lead. (The electrodes attach with the metal facing down.)
For Channel 1 (Horizontal Measurement) / For Channel 2 (Vertical measurement)Black
/ Connect to electrode in middle of forehead / Connect to second electrode in middle of forehead (Note: this is the one incorrectly placed in the earlier illustrations. Did you detect it?Red
/ Connect to electrode next to Right eye / Connect to electrode above Right eyeWhite
/ Connect to electrode next to Left eye / Connect to electrode belowRight eye
Figure 12. The typical hook up of Electro-oculogram (EOG) electrodes for BioPac Lab 10 (NOTE: Do you see which electrode is misplaced, and where it should be placed? You will need to in order to collect accurate data.).
8. Have Participant (i.e., researcher B) adjust the seating position such that his/her eyes are in line with the center of the computer screen. Be sure that the distance from the eyes to the screen is approximately at arm’s length (have Participant reach).