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Related Concept Videos

Reaction Rate02:53

Reaction Rate

The rate of reaction is the change in the amount of a reactant or product per unit time. Reaction rates are therefore determined by measuring the time dependence of some property that can be related to reactant or product amounts. Rates of reactions that consume or produce gaseous substances, for example, are conveniently determined by measuring changes in volume or pressure.
The mathematical representation of the change in the concentration of reactants and products, over time, is the rate...
Rate Law and Reaction Order02:33

Rate Law and Reaction Order

The rate of a reaction is affected by the concentrations of reactants. Rate laws (differential rate laws) or rate equations are mathematical expressions describing the relationship between the rate of a chemical reaction and the concentration of its reactants.
For example, in a generic reaction aA + bB ⟶ products, where a and b are stoichiometric coefficients, the rate law can be written as:
rate = k[A]m[B]n
[A] and [B] represent the molar concentrations of reactants, and k is the rate...
Factors Influencing the Rate of Chemical Reactions01:22

Factors Influencing the Rate of Chemical Reactions

A variety of factors influence the rate of chemical reactions. For a chemical reaction to happen, atoms must collide with enough energy to overcome the repulsion between their electrons. This energy is called activation energy. Factors influencing the rate of reaction either lower the activation energy or increase the likelihood of a successful collision.
Concentration and Pressure:
The more particles present within a given space, the more likely those particles are to bump into one another.
Determining Order of Reaction02:53

Determining Order of Reaction

Rate laws describe the relationship between the rate of a chemical reaction and the concentration of its reactants. In a rate law, the rate constant k and the reaction orders are determined experimentally by observing how the rate of reaction changes as the concentrations of the reactants are changed. A common experimental approach to the determination of rate laws is the method of initial rates. This method involves measuring reaction rates for multiple experimental trials carried out using...
Effect of Temperature Change on Reaction Rate02:28

Effect of Temperature Change on Reaction Rate

The Arrhenius equation,
Temperature Dependence on Reaction Rate02:55

Temperature Dependence on Reaction Rate

The Collision Theory
Atoms, molecules, or ions must collide before they can react with each other. Atoms must be close together to form chemical bonds. This premise is the basis for a theory that explains many observations regarding chemical kinetics, including factors affecting reaction rates.
The collision theory is based on the postulates that (i) the reaction rate is proportional to the rate of reactant collisions, (ii) the reacting species collide in an orientation allowing contact between...

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Related Experiment Video

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Measuring Attention and Visual Processing Speed by Model-based Analysis of Temporal-order Judgments
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Measuring Attention and Visual Processing Speed by Model-based Analysis of Temporal-order Judgments

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A priori probability effects on simple reaction time.

E Buckolz1, R Wilberg

  • 1a Departement Education Physique , Universite de Montreal.

Journal of Motor Behavior
|August 22, 2013
PubMed
Summary
This summary is machine-generated.

This study on simple reaction time (RT) found that a priori probability, not foreknowledge, influences RT. Knowing what to expect, rather than uncertainty, is key to faster responses.

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Area of Science:

  • Cognitive psychology
  • Human reaction time studies
  • Psychophysics

Background:

  • Reaction time (RT) is influenced by foreperiod duration and predictability.
  • Previous research suggests an inverse relationship between simple RT and foreperiod length.
  • The role of a priori probability versus foreknowledge in RT control requires further investigation.

Purpose of the Study:

  • To investigate whether a priori probability independently affects simple RT.
  • To examine the relationship between a priori probability, previous foreperiod effects, and foreperiod length.
  • To determine whether knowledge or uncertainty primarily controls simple RT.

Main Methods:

  • Utilized a variable foreperiod simple reaction time (RT) design.
  • Manipulated three factors: immediate foreperiod length (1.0 and 4.0 sec), previous foreperiod length (1.0 and 4.0 sec), and a priori probability (0.8 and 0.2).

Main Results:

  • Confirmed that a priori probability functions independently of previous foreperiod effects.
  • Demonstrated that knowledge of upcoming stimuli, not uncertainty, is the primary controller of simple RT.
  • Supported the hypothesis explaining the inverse relationship between simple RT and foreperiod length.

Conclusions:

  • A priori probability is a significant, independent factor in simple RT.
  • Subjective knowledge, rather than lack of knowledge, dictates reaction time.
  • Findings clarify the mechanisms underlying foreperiod effects in RT tasks.