I'm writing a novel in which the main character's perception and thought processes are sped up considerably, in essence slowing down the world around him. To others, it seems like his reactions are far faster than normal. Of course, there's a fantasy explanation for this in the story, but it led me to wonder exactly what limits the speed of human perception and reasoning in the real world.

From what I know, the speed at which we perceive events appears to be a constant. What exactly determines that rate? Is it possible to change it? Is it possible that different people perceive things at different speeds?

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    $\begingroup$ Actually there is a movie on this concept- Limitless.. You can check this post. You may find it useful. $\endgroup$ – WYSIWYG Jul 24 '14 at 4:54
  • $\begingroup$ The vertebrate photoreceptors may have a certain speed threshold, so you can give him mutant fly photoreceptors. Chimpanzees can see 10 different objects on a screen and choose one of them much faster than a human, perhaps it's to do with peripheral vision. you can have mutant connections between the old and new areas of the brain which can learn reflexes perfectly. $\endgroup$ – com.prehensible Feb 26 at 10:47

Flicker Fusion Threshold:

The wikipedia definition:

It is defined as the frequency at which an intermittent light stimulus appears to be completely steady to the average human observer.


In 1824, Peter Mark Roget (who also wrote the famous Thesaurus) first presented the concept of "persistence of vision" to the Royal Society of London, as the ability of the retina to retain an image of an object for $\frac{1}{20}$ to $\frac{1}{5}$ second after its removal from the field of vision.

A second principle - the $\phi\ phenomenon$ or stroboscopic effect is closely related to flicker fusion. It was first studied by Max Wertheimer and Hugo Munsterberg between 1912-16. Wertheimer and Munsterberg found that subjects can perceptually bridge the temporal gap between two consecutive displays, so that a series of static images appear as continuous movement. The discovery of flicker fusion became the perceptual basis for moving pictures, television, and all media based on stroboscopic presentation of stimuli.

The minimal frequency at which flickering stimuli appear continuous is called the critical flicker frequency.

Perceptual factors affecting the critical flicker fusion threshold

This critical flicker fusion threshold depends on the stimulus’

  • Luminance (the Ferry-Porter law),
  • Size (the Granit-Harper law),
  • Color,
  • Retinal eccentricity,
  • Background Luminance, and other factors.

Biology Behind it:

Physiological evidence in humans and monkeys shows that flicker rates above the perceptual critical flicker frequency threshold can nevertheless generate cortical and subcortical visual responses. Thus the temporal integration underlying flicker fusion does not occur at the level of the retina, but must take place later in the visual hierarchy. Single-unit recordings in the primary visual cortex of primates suggests that, for two brief-duration targets presented in close succession, the after-discharge to the first target interferes with the onset-response to the second target (Macknik, 2006) (see Figure 5). The onset-response to the second flash is absent for inter-stimuli intervals of 30 msec or shorter (equivalent to 17 Hz periodic). If the flashes are separated by more than 30 ms, the after-discharge to the first flash and the onset-response to the second flash begin to recover (i.e. equivalent to <17 Hz flicker). These intervals roughly coincide with the critical flicker fusion threshold in humans for 100% contrast stimuli in the fovea .

This suggests that perceptual flicker fusion may be due to the lack of robust transient responses to the flickering stimulus.



  • Bartley (1939). Some effects of intermittent photic stimulation. Journal of Experimental Psychology 25, 462-480.
  • Bloch, A. M. (1885). Experience sur la vision. Comptes Rendus de Seances de la Societe de Biologie, Paris 37, 493-495.
  • Brücke, E. (1864). Über den Nutzeffect intermittierender Netzhautreizungen. Sitzungsber k Akad Wissensch Math-naturw Cl, Wien 49, 128-153.
  • Di Lollo, V., and Bischof, W. F. (1995). Inverse-intensity effect in duration of visible persistence. Psychol Bull 118, 223-237.
  • Ferry, E. (1892). Persistence of vision. Amer J Sci 44, 192-207.
  • Fukuda, T. (1979). Relation between flicker fusion threshold and retinal positions. Percept Mot Skills 49, 3-17.
  • Flicker Fusion

What is the Different speeds of Visual Perception?

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First-order motion

Experiment: A moving sinusoidal grating with bright peaks and dark troughs is seen through a window.

Result: Even when its velocity is so high that 30 of its bright peaks pass each location per second (30 Hz), observers still perceive its direction of motion.

Depth from binocular disparity

Experiment: Two identical gratings, one in each eye, are viewed through identical windows.

Result: One is spatially shifted relative to the other, introducing a binocular disparity that is perceived as depth. Even when they move at a 30 Hz rate, the depth is still perceived. If the input to depth mechanisms were blurred at a >30 ms timescale, detecting the depth would be impossible at this rate.

Edges and texture boundaries

Experiment: Against a gray background, a field of white dots is adjacent to a field of black dots.

Result: Both fields are set in rapid alternation between white and black, but out of phase – when one is white, the other is black. The conspicuous boundary between them is perceived even at fast rates of 30 Hz, whereas at faster rates the black and white are averaged by the brain into the same color as the background.


Binding of color and orientation sharing a spatial location

Experiment & Result: If a red, right-tilted patch is alternated with a green, left tilted patch, it is easy to distinguish from the complementary pairing of red left alternating with green right, even at fast 20 Hz rates.

Binding of form and color across space

Alternating color-shape pairings can only be reported at rates below ~3 Hz.

source: http://www.psych.usyd.edu.au/staff/colinc/HTML/dynamics.htm

Binding of global form with color

Two specially constructed dot patterns that form distinct shapes alternate, with all the dots of one red and all the dots of the other green.

At alternation rates faster than several a second it is very difficult to determine the shape color pairing even though the shapes and colors themselves are easily identified.

Direction change and acceleration perception

A moving stimulus alternates between two speeds (acceleration) or two directions. When the alternation occurs faster than several per second, these changes are unperceivable. Its limit is 8-10 Hz.

Word perception

Certain pairs of words (such as ‘jump’ and ‘pink’), when alternated in the same location, cannot be distinguished from another matched pair at rapid rates as one perceives only the sum, which is the same for both pairs. They can be distinguished only at rates slower than several items per second.

Source: http://www.psych.usyd.edu.au/staff/alexh/research/words/


  1. Holcombe AO (2009) Seeing slow and seeing fast: two limits on perception. Trends Cogn Sci 13:216 –221.
  2. http://www.psych.usyd.edu.au/staff/colinc/HTML/dynamics.htm
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    $\begingroup$ Hi, nice response! but I'm still wondering which part in your response shows the limiting factors/reasons behind the human perception speed limitation. You have a very nice list of perception/cognitive limitations but not the underlying reason. Are there explanations for these limitations that can be elaborated through neurophysiology or molecular biology perhaps? $\endgroup$ – Bez Jul 24 '14 at 16:53
  • $\begingroup$ Definitely some interesting material that you've shared here, Devashish Das, but I also would be interested in the underlying reasons that the human perception rate is limited. You don't seem to have talked about that too much here--looking forward to hearing more from you. $\endgroup$ – Elliot Bonneville Jul 25 '14 at 3:15
  • $\begingroup$ @Bez: Oh Sorry!! You were asking about Flicker fusion threshold!!! $\endgroup$ – Devashish Das Jul 25 '14 at 6:17

The limitations are of several natures: cognitive once the signal has arrived in the brain, but also physical within the eye e.g. for vision.

For vision, the crucial bit is to transform changes of incoming light into an electrical signal. It is not completely elucidated. Recent research shows e.g. that for some flies, there may be a mechanical intermediate stage: the light-sensing cells react by contracting, and this would modify the electric resistance of their membrane. I don't think it is known whether the human, who have less need for a fast response but want more detail of what they're looking at, have the same mechanism or not: maybe your hero has something of the fly that we don't have?


Here's a paper on the link between perception and reaction time. The general theme in biology is that the greater number of neurons an animal has in series, the more latency that animal will have in that pathway. This can partially account for organisms which have tiny nervous systems and very quick reflexes.

In our own body, we have reflex pathways which entirely circumvent our brain. These help us maintain our posture and remain upright. These are muscle spindles and spinal reflexes. They are among the quickest response mechanisms.

You might want to look up synaptic pruning and synesthesia. These are two phenomena on opposite ends of the spectrum of synapse count. Synesthesia is an excess of sensory pathways in the brain and synaptic pruning is the natural deletion of pathways in the maturing brain.

Most of our movements are variations on muscle memories, mediated by the cerebellum. You can start your research on muscle memory here. Developing muscle memory is a rigorous process, but is a fundamental learning tool for musicians and those in martial arts.


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