Ideal Observer Analysis
Encyclopedia
Ideal observer analysis is a method for investigating how information is processed in a perceptual system
. It is also a basic principle that guides modern research in perception
.
The ideal observer is a theoretical system that performs a specific task in an optimal way. If there is uncertainty in the task, then perfect performance is impossible and the ideal observer will make errors.
Ideal performance is the theoretical upper limit of performance. It is theoretically impossible for a real system to perform better than ideal. Typically, real systems are only capable of sub-ideal performance.
This technique is useful for analyzing psychophysical data (see psychophysics
).
Geisler (2003) (slightly reworded): The central concept in ideal observer analysis is the ideal observer, a theoretical device that performs a given task in an optimal fashion given the available information and some specified constraints. This is not to say that ideal observers perform without error, but rather that they perform at the physical limit of what is possible in the situation. The fundamental role of uncertainty and noise implies that ideal observers must be defined in probabilistic (statistical) terms. Ideal observer analysis involves determining the performance of the ideal observer in a given task and then comparing its performance to that of a real perceptual system, which (depending on the application) might be the system as a whole, a subsystem, or an elementary component of the system (e.g. a neuron).
.
In such cases, it may be important to keep the system operating naturally (or almost naturally) by designing a pseudo-natural task. Such tasks are still artificial, but they attempt to mimic the natural demands placed on a system. For example, the task might employ stimuli that resemble natural scenes
and might test the system's ability to make potentially useful judgments about these stimuli.
Natural scene statistics
are the basis for calculating ideal performance in natural and pseudo-natural tasks. This calculation tends to incorporate elements of signal detection theory
, information theory
, or estimation theory
.
Perceptual system
A perceptual system is a computational system designed to make inferences about properties of a physical environment based on scenes. Other definitions may exist....
. It is also a basic principle that guides modern research in perception
Perception
Perception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...
.
The ideal observer is a theoretical system that performs a specific task in an optimal way. If there is uncertainty in the task, then perfect performance is impossible and the ideal observer will make errors.
Ideal performance is the theoretical upper limit of performance. It is theoretically impossible for a real system to perform better than ideal. Typically, real systems are only capable of sub-ideal performance.
This technique is useful for analyzing psychophysical data (see psychophysics
Psychophysics
Psychophysics quantitatively investigates the relationship between physical stimuli and the sensations and perceptions they effect. Psychophysics has been described as "the scientific study of the relation between stimulus and sensation" or, more completely, as "the analysis of perceptual...
).
Definition
Many definitions of this term have been offered.Geisler (2003) (slightly reworded): The central concept in ideal observer analysis is the ideal observer, a theoretical device that performs a given task in an optimal fashion given the available information and some specified constraints. This is not to say that ideal observers perform without error, but rather that they perform at the physical limit of what is possible in the situation. The fundamental role of uncertainty and noise implies that ideal observers must be defined in probabilistic (statistical) terms. Ideal observer analysis involves determining the performance of the ideal observer in a given task and then comparing its performance to that of a real perceptual system, which (depending on the application) might be the system as a whole, a subsystem, or an elementary component of the system (e.g. a neuron).
Sequential ideal observer analysis
In sequential ideal observer analysis, the goal is to measure a real system's performance deficit (relative to ideal) at different processing stages. Such an approach is useful when studying systems that process information in discrete (or semi-discrete) stages or modules.Natural and pseudo-natural tasks
To facilitate experimental design in the laboratory, an artificial task may be designed so that the system's performance in the task may be studied. If the task is too artificial, the system may be pushed away from a natural mode of operation. Depending on the goals of the experiment, this may diminish its external validityExternal validity
External validity is the validity of generalized inferences in scientific studies, usually based on experiments as experimental validity....
.
In such cases, it may be important to keep the system operating naturally (or almost naturally) by designing a pseudo-natural task. Such tasks are still artificial, but they attempt to mimic the natural demands placed on a system. For example, the task might employ stimuli that resemble natural scenes
Scene (perception)
In the field of perception, a scene is information that can flow from a physical environment into a perceptual system via sensory transduction....
and might test the system's ability to make potentially useful judgments about these stimuli.
Natural scene statistics
Scene statistics
Scene statistics is a discipline within the field of perception. It is concerned with the statistical regularities related to scenes. It is based on the premise that a perceptual system is designed to interpret scenes....
are the basis for calculating ideal performance in natural and pseudo-natural tasks. This calculation tends to incorporate elements of signal detection theory
Detection theory
Detection theory, or signal detection theory, is a means to quantify the ability to discern between information-bearing energy patterns and random energy patterns that distract from the information Detection theory, or signal detection theory, is a means to quantify the ability to discern between...
, information theory
Information theory
Information theory is a branch of applied mathematics and electrical engineering involving the quantification of information. Information theory was developed by Claude E. Shannon to find fundamental limits on signal processing operations such as compressing data and on reliably storing and...
, or estimation theory
Estimation theory
Estimation theory is a branch of statistics and signal processing that deals with estimating the values of parameters based on measured/empirical data that has a random component. The parameters describe an underlying physical setting in such a way that their value affects the distribution of the...
.