Kappa effect: what is this phenomenon of perception?

The Kappa effect is a perceptual illusion, and it is further proof that our minds and senses sometimes deceive us.

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

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What is basic psychology?

Basic psychology is a part of psychology in charge of study 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 investigates 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 that occurs with 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 "perceptual time dilation", and consists of an illusion of perception, which is temporary, and which arises when people who observe a series of sensory stimuli that occur sequentially, in different places, judge how much time has elapsed between stimulus and stimulus.

Observers, upon perceiving a sequence of stimuli consecutively, they tend to overestimate the time that has elapsed between successive stimuli when the distance between them is large enough; conversely, when the distance is small enough, observers tend to underestimate the time elapsed between stimuli.

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Sensory modalities

The Kappa effect can be produced with three types of sensory modalities: visual modality (visual stimuli, such as flashes of light), auditory modality (such as tones), and tactile modality (for example bumps on the skin).

1. Visual

Most of the studies carried out on the Kappa effect have been carried out with the visual modality, that is, with visual stimuli. To better illustrate this effect, let's think about the following: three light sources, named A, B, and C, which light up in succession in the dark. The interval between stimulus and stimulus is the same between each of them.

Now imagine that we place these three light sources, A, B and C, in different positions (for example A and B closer together than B and C); If we do so, the observer will perceive that the time interval between the flash of A and B (these sources are closer), is shorter than the time interval between flashes of B and C (these sources are farther between they).

2. Auditory

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

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

In other words, the observers perceived a shorter time interval in the face of increasingly separated stimuli (that is, they perceived that less time was spent between them).

Explanatory theories of this perceptual illusion

What theories try to explain the Kappa effect? Theories that incorporate the element of speed, since this it is the element that “unites” 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 are going to know the three theories that try to explain the Kappa effect, explained in a very summarized way:

1. Low speed expectation

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

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. Constant speed expectation

The second explanatory theory of the Kappa effect, basically what it says is that our brain has established the expectation that the speed of the stimuli (that is, the time between stimulus and stimulus) will be constant. This expectation, logically, leads us to commit perceptual "errors", and that is why the Kappa effect would occur..

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 were appearing successively, in a certain direction (horizontal) along the aforementioned straight line.

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

On the other hand, when the time interval between stimulus and stimulus was modified under the experimental conditions, as well as its physical separation, the Kappa effect was not observed (the hypothesis of the velocity constant).

What explanation did the researchers offer for this? Basically, it is not easy to perceive a 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 observers' temporal perception (that is, the time we perceive that elapses between stimulus and stimulus).

3. Movement in different contexts

The third theory that claims to explain the Kappa effect is the theory of motion in different contexts. According to this theory, the higher the speed of the stimuli, the greater the resulting Kappa effectand.

This theory also maintains 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 towards under.

How do you explain this? The researchers proposed that we have the prior expectation that the acceleration is downward, and that the deceleration is upward; As a result of this, it follows that we underestimate the time interval between stimuli (that is, we believe that they go faster than they actually go).

Bibliographic references:

• Goldstein, E.B. (2006). Sensation and perception. 6th edition. Debate. Madrid.
• Henry, M.J. & McAuley, J.D. (2009). "Evaluation of an imputed tone velocity model of the auditory kappa 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 temporal auditory processing with a single stimulus method. Advances in the localization of sound, 95-104.