The Kappa effect is a perceptive illusion , and constitutes one more proof that, sometimes, our mind and our senses deceive us.

In this article we will see what this phenomenon consists of, how it has been studied, to what type of sensory modalities it can be applied and what theories try to explain it. As we will see, this perceptive phenomenon is part of a branch of psychology, basic psychology.

What is basic psychology?

Basic psychology is a part of psychology that studies a series of psychological and behavioral processes, as well as the laws that govern these processes . The main areas in which this branch of psychology researches are: perception, sensation, learning, reasoning, motivation and memory.

Within the area of perception, we find a series of perceptual illusions, which “deceive” our mind. One of these illusions is the Kappa effect which is produced before different types of stimuli, and which we will see below.

What is the Kappa effect?

The Kappa effect is a phenomenon of basic psychology; it is also called “dilation of perceptual time”, and consists of an illusion of perception, which is temporary, and which arises when people who observe a series of sensory stimuli occurring sequentially, in different places, judge how much time has elapsed between stimulus and stimulus .

Observers, perceiving a sequence of stimuli consecutively, tend to overestimate the time that has passed between successive stimuli when the distance between them is sufficiently large ; in contrast, when the distance is small enough, observers tend to underestimate the time that has passed between stimuli.

Sensory modes

The Kappa effect can be produced with three types of sensory modes: the visual mode (visual stimuli, such as flashes of light), the auditory mode (e.g. tones) and the tactile mode (e.g. hits on the skin).

1. Visual

Most of the studies developed on the Kappa effect have been carried out with the visual mode, that is, with visual stimuli. To better illustrate this effect, let us think of the following: three sources of light, called A, B and C, which light up successively in the dark. The interval between stimulus and stimulus is equal between each of them.

Now let’s imagine that we place these three light sources, A, B and C, in different positions (for example, A and B more closely than B and C); if we do so, the observer will perceive that the time interval between the flashes of A and B (these sources are closer), is shorter than the time interval between the flashes of B and C (these sources are further apart).

2. Auditory

In the auditory modality (with auditory stimuli), the Kappa effect has also been demonstrated , although not in all experimental paradigms.

To cite an example, in an experiment conducted by Roy et al. (2011), it was found just the opposite; that when the distance between different sound sources (auditory stimuli) was increased, the time intervals perceived by the observer, between source and source, were smaller.

In other words, observers perceived a shorter time interval in the face of increasingly separate stimuli (i.e., they perceived less time spent with each other).

Explanatory theories of this perceptual illusion

What theories try to explain the Kappa effect? Theories that incorporate the element of speed, since speed is the element that “binds” the space between stimulus and stimulus and the time interval between them .

Specifically, these theories focus on the brain’s expectations regarding the speed between stimuli. We will know the three theories that try to explain the Kappa effect, explained in a very summarized way:

1. Expectation of low speed

The first theory we’re going to explain is that of low-speed expectation. This is based on a model, called the Bayesian perceptual model, and aims to explain the Kappa effect on tactile stimuli .

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This theory states that brain circuits encode the expectation that tactile stimuli move slowly. This expectation results in us overestimating the time that elapses between the appearance of stimulus and stimulus.

2. Expectation of constant speed

The second theory explaining the Kappa effect basically says that our brain has an expectation that the speed of stimuli (i.e., the time between stimuli) will be constant. This expectation, logically, leads us to make perceptive “errors”, and that is why the Kappa effect would be produced .

This theory tried to explain the Kappa effect through a study, which consisted of the following: different participants observed a total of eight white points, in a straight line; these points appeared successively, in a certain direction (horizontal) along the mentioned straight line.

What happened? That when the time interval between stimulus and stimulus (that is, between their appearance) was constant , and their physical separation varied, the Kappa effect was produced (following the hypothesis or theory of constant velocity).

However, when the time interval between stimuli and their physical separation was changed under experimental conditions, the Kappa effect was not observed (the hypothesis of constant speed was not fulfilled).

What explanation did the researchers offer for this? Basically that it is not easy to perceive uniform movement when the patterns are so diverse and complicated. In this way, they determined how the context of presentation of the stimuli could affect the temporal perception of the observers (i.e., the time we perceive as passing between stimuli).

3. Movement in different contexts

The third theory that aims to explain the Kappa effect is the theory of movement in different contexts. According to this theory, the greater the speed of the stimuli, the greater the resultant Kappa effect e.

This theory also holds that observers have the tendency to apply their previous knowledge in relation to movement, to a certain sequence of stimuli; thus, in different studies, it was observed how, at the moment in which the participants observed stimuli placed vertically, the Kappa effect was greater in the sequences that moved downwards.

How do you explain this? The researchers proposed that we have the prior expectation that acceleration occurs downwards, and that deceleration occurs upwards ; as a result, it follows that we underestimate the time interval between stimuli (i.e., that we believe that they go faster than they actually do).

Bibliographic references:

  • Goldstein, E.B. (2006). Sensation and perception. 6th edition. Debate. Madrid.
  • Henry, M.J. & McAuley, J.D. (2009). “Evaluation of an imputed pitch velocity model of the kappa auditory effect.” Journal of experimental psychology: human perception and performance . 35 (2): 551–64.
  • Masuda, T., Kimura, A., Dan, I. & Wada, Y. (2011). Effects of environmental context on temporal perception bias in apparent movement ” Vision Research 51, 1728-1740.
  • Roy, M., Kuroda, T. & Grondin, S. (2011). Effect of space on auditory temporal processing with a unique stimulus method. Advances in sound localization, 95-104.