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Blind Procedures

Blind Procedures

Ideally, the people who observe and record the children’s behavior are unaware of who was assigned to the experimental or control group, in order to control for experimenter bias. Experimenter bias refers to the possibility that a researcher’s expectations might skew the results of the study. Remember, conducting an experiment requires a lot of planning, and the people involved in the research project have a vested interest in supporting their hypotheses. If the observers knew which child was...

Blinding

Blinding

Blinding is a commonly used method of not telling participants which treatment a subject is receiving. Blinding is a critical part of a randomized control trial or RCT. It reduces the bias that affects the results. In an RCT, blinding is used in the form of a placebo. A placebo effect occurs when untreated subjects falsely believe they have received the treatment and report improved symptoms. A placebo or a dummy treatment is administered to subjects to negate the bias caused by such an effect.

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Related Experiment Video

Updated: May 10, 2026

Assessing Pupil-linked Changes in Locus Coeruleus-mediated Arousal Elicited by Trigeminal Stimulation

Assessing Pupil-linked Changes in Locus Coeruleus-mediated Arousal Elicited by Trigeminal Stimulation

Published on: November 26, 2019

A confound-free method to manipulate pupil size in psychological experiments.

Joshua Snell¹, Luise Wagner², Ana Vilotijević³

¹Department of Experimental and Applied Psychology, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands. J.J.Snell@VU.nl.

Psychonomic Bulletin & Review

|February 18, 2026

Summary

This study validates a method using blue light to control pupil size via intrinsically photosensitive retinal ganglion cells (ipRGCs). The findings confirm that display color affects pupil size but not cognitive task performance, ensuring reliable pupil-based research.

Keywords:

Arousal Effort IpRGC Pupil size Pupillometry

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Last Updated: May 10, 2026

Assessing Pupil-linked Changes in Locus Coeruleus-mediated Arousal Elicited by Trigeminal Stimulation

Assessing Pupil-linked Changes in Locus Coeruleus-mediated Arousal Elicited by Trigeminal Stimulation

Published on: November 26, 2019

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Published on: January 6, 2023

Author Spotlight: An Accurate and Quantitative Approach to Study Visual Feature Selectivity of the Optokinetic Reflex in Mice

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Published on: June 23, 2023

Area of Science:

Cognitive Neuroscience
Ophthalmology
Psychology

Background:

Pupil size influences cognitive processes, but research is confounded by factors affecting pupil dilation.
Intrinsically photosensitive retinal ganglion cells (ipRGCs) offer a method to control pupil size using blue light.
Potential confounding effects of blue vs. red light on alertness and arousal require investigation.

Purpose of the Study:

To validate a method for controlling pupil size using blue light stimuli.
To investigate whether blue vs. red light backgrounds differentially affect cognitive task performance.
To ensure the reliability of using ipRGCs for pupil-modulated cognitive research.

Main Methods:

Participants performed an auditory reaction time task under blue and red visual displays of equal luminance.
Task difficulty was manipulated (easy and difficult versions).
Pupil size and task performance were measured.

Main Results:

Task difficulty significantly affected both pupil size and performance.
Display color (blue vs. red) significantly affected pupil size.
Display color did not significantly affect task performance, independent of task difficulty.

Conclusions:

The ipRGC-based method for manipulating pupil size is validated.
Differential effects of blue and red light on alertness do not confound pupil-based cognitive research.
This method reliably isolates the effect of pupil size on cognition.