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Related Experiment Video

Updated: Jun 21, 2026

A Two-interval Forced-choice Task for Multisensory Comparisons

A Two-interval Forced-choice Task for Multisensory Comparisons

Published on: November 9, 2018

Fixed vs. variable noise in 2AFC contrast discrimination: lessons from psychometric functions.

Miguel A García-Pérez¹, Rocío Alcalá-Quintana

¹Departamento de Metodología, Facultad de Psicología, Universidad Complutense, Campus de Somosaguas, 28223 Madrid, Spain. miguel@psi.ucm.es

|July 23, 2009

Summary

The nature of noise limiting 2AFC discrimination performance cannot be determined by fitting models to data. Both fixed and variable noise models can equally fit performance data, regardless of experimental methods.

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Area of Science:

Psychophysics
Computational Neuroscience
Sensory Perception

Background:

The nature of internal noise is crucial for understanding sensory discrimination limits.
Distinguishing between fixed and variable noise has been a focus of recent psychophysical research.

Purpose of the Study:

To demonstrate that goodness-of-fit statistics cannot resolve whether sensory noise is fixed or variable.
To analyze the limitations of model fitting in psychophysical research.

Main Methods:

Theoretical analysis of model fitting in psychophysics.
Examination of how transducer functions interact with noise models.
Critique of experimental methods aimed at dissociating response mean and variance.

Main Results:

Data from detection and discrimination tasks can be fitted equally well by models assuming either fixed or variable noise.
Model fitting success is dependent on the chosen transducer function, not the noise type.
Goodness-of-fit does not reveal the underlying nature of sensory noise.

Conclusions:

The question of fixed versus variable noise cannot be solved by fitting models to performance data.
Further theoretical and experimental advancements are needed to characterize sensory noise.