Experimental variables

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Eye tracking experiment hypothesis and variables

Resource Details

  • Written by

    Ieva Miseviciute

  • Read time

    4 min

Scientific research is one of the central forces propelling global progress. It fosters innovation, offers solutions to complex problems, and enhances the quality of life across various domains, like technology, healthcare, and public policy. Science-driven improvements begin with curiosity and the desire to unravel the world’s mysteries or put theoretical, sometimes even anecdotal, assumptions to the test.

Eye tracking is a behavioral research tool often used to answer research questions about various aspects of human behavior and cognition, such as visual attention, memory, or decision-making.

Here are some examples of research questions that can be addressed with eye tracking:

  • How does watching a horror movie affect the autonomic nervous system?
  • Do eye movements influence memory retrieval?
  • Does blinking affect the perception of time?

Hypothesis, independent and dependent variables

As illustrated above, research questions are too broad to answer in a controlled and systematic manner. Therefore, they require dissection into testable hypotheses. The hypothesis is the prediction about a possible outcome of an experiment where an independent variable is manipulated, and the corresponding change in a dependent variable will be observed. Researchers formulate hypotheses based on existing knowledge and then design experiments to either confirm or refute these hypotheses.

Independent variables:

Factors or conditions an experimenter manipulates in an experiment. The hypothesis suggests that changing this variable causes a direct effect on the dependent variable.

Dependent variables:

Factor or condition observed or measured in response to manipulations in the independent variable.

Experimental variables
The relationship between the independent and dependent variables.

Here are some examples of experiment hypothesis and its independent and dependent variables:

·  Hypothesis: Watching a horror movie clip will cause an increase in pupil size compared to watching a neutral movie clip.

Independent variable:

Type of movie clip (horror or neutral).

Dependent variable:

Pupil size.

·  Hypothesis: Saccades during memory encoding will lead to better memory performance.

Independent variable:

Saccades during memory encoding.

Dependent variable:

Memory performance.

·  Hypothesis: A higher blinking rate during an auditory stimulus will result in the perception of the stimulus duration as longer (overestimation).

Independent variable:

Blinking rate during the auditory stimulus

Dependent variable:

The perceived duration of the auditory stimulus.

Extraneous variables

Some additional types of variables are important to consider when designing an eye tracking experiment:

Extraneous variables (also known as confounding variables)

Factors or conditions that may affect the outcome of an experiment, even though they are not the primary independent or dependent variables. Extraneous variables may introduce unwanted bias in your data and lead to inaccurate conclusions. Extraneous variables can be controlled and uncontrolled.

  • Controlled variables are kept constant or controlled during the experiment. This is usually achieved by randomization, matching, or counterbalancing controlled extraneous variables.
  • Uncontrolled variables can affect study results but are not intentionally controlled or accounted for in the study design. Uncontrolled extraneous variables make it difficult to determine if the observed effects are due to independent variables or other factors.

In the experiment studying "The link between saccades and memory performance,” these are some extraneous variables to consider:

Controlled extraneous variables

  • Room environment: temperature, humidity, noise level, light levels.
  • Differences in participant characteristics: age, gender, education.
  • Order of stimulus presentation – low saccade scenes counterbalanced with high saccade scenes.
  • Time of the day to prevent variations due to circadian rhythms.

Uncontrolled extraneous variables

  • Emotional states or mood at the time of the experiment might impact memory.
  • Visual fatigue – might affect a number of saccades and recall quality.
  • Distractions – unforeseen noise from outside the experiment room.
  • Individual differences in memory capacity.
Experimental variables
The effect of extraneous variables on the relationship between the independent and dependent variables.

Participant and stimulus variables

Participant variables

Different individual characteristics that may impact how a participant responds in an experiment. Examples of participant variables include gender, age, ethnicity, socioeconomic status, literacy status, mood, clinical diagnosis, and others.

Stimulus variables

Features of your stimulus or group of stimuli that are part of the context in which the behavior occurs. These are often an expression of or a subset of independent variables and covariates. Examples include the number of items, category, stimulus crowdedness, color, brightness, and contrast.

Variable operationalization – an essential step in preparation for an experiment

Before starting your experiment, it is essential to have a clear definition of and strategy for how each variable will be measured and recorded. This process is called variable operationalization. For your experiment investigating “The link between saccades and memory performance,” you will need to operationalize two primary variables:

Saccades (Independent Variable)

The number of saccades refers to the count of rapid, ballistic eye movements that occur when an individual views a visual scene. Define what aspects of saccades you are interested in, for example – saccade amplitude toward AOIs, number of saccades, or scan path.

To manipulate the presence of saccades, you can introduce a stimulus variable – trials in which participants are asked to fixate on a screen during the entire stimulus viewing period. In this way, you can account for the effect of saccades on memory retrieval by comparing ”saccade trials” to ”fixation trials.” Learn more about different
types of eye movements.

To measure, record, and quantify various aspects of saccades and fixations, you can use eye tracking technology, such as eye tracking software and hardware.
Tobii eye trackers can capture eye movement data at up to 1200 Hz, and the
Tobii Pro Lab software simplifies the calculation and export of various eye tracking metrics.

Eye tracking – a window to cognitive processes

Curious to learn more about eye tracking in scientific research? This white paper explains how eye tracking can provide insights into attention, memory, decision-making, problem-solving, and more.

Memory Performance (Dependent Variable)

Define what aspects of memory performance you want to quantify and the tasks you will use. Will you use recall tasks, recognition tasks, or retrieval? Variables related to the memory performance measurement might include:

  • Memory task type (e.g., free recall, cued recall, recognition).
  • Stimulus materials (e.g., words, images, or other types of information).
  • Presentation format (e.g., visual, auditory, or both).
  • Memory aspects (e.g., speed, accuracy, or both).

Resource Details

  • Written by

    Ieva Miseviciute

  • Read time

    4 min

    Resource type

    • Learn article

    Tagged products

    • Software
    • Eye trackers

    Tagged solutions

    • Scientific research


  • Tobii employee

    Ieva Miseviciute, Ph.D.


    As a science writer, I get to read peer-reviewed publications and write about the use of eye tracking in scientific research. I love discovering the new ways in which eye tracking advances our understanding of human cognition.

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