44 votes
Accepted

Are drugs made bitter artificially to prevent being mistaken for candy?

Short answer A bittering agent may be applied to therapeuticals to prevent pediatric poisonings, but many drugs inherently taste bitter by themselves. Background Bitter taste is thought to have ...
  • 51.5k
36 votes
Accepted

Why does my room suddenly look 'reddish'? My eyes seem to adapt to color

Short answer The phenomenon you describe can be explained by the negative afterimage effect, which indeed is elicited by adaptive processes in the retinae. Background In the retina there are three ...
  • 51.5k
33 votes
Accepted

Can one see flickering of a light bulb at 50 Hz?

Short answer Yes, the flickering of a light bulb may be noticeable, and yes, that's directly related to the mains frequency. However, since the flickering of a bulb is about two times higher than the ...
  • 51.5k
30 votes
Accepted

Why do mints make your mouth feel cold?

The feeling of cold from mints is caused by menthol. Menthol affects the TRPM8 receptor on skin and also in the mouth. TRPM8 is also a general cold receptor: so if you are in contact with menthol the ...
  • 2,878
21 votes

Are some animals, like dogs and cats, color-blind and how do we know that?

TL;DR: We have a good physiological understanding of how eyes work, so by examination of other species' eyes, we can tell a lot about what colours they are capable of seeing. First, a little bit ...
  • 3,294
14 votes
Accepted

Why is wind cold for humans?

One important point that you might not be considering is the heat of vaporization. You may be aware that while it normally takes 4.18 J (1 calorie) of heat to raise 1 gram of water 1 °C, it takes ...
  • 1,544
12 votes

What is the science behind the inaccurate perception of colors?

First recall that pink is white minus green, more or less. Now, your perception can be explained by adaptation: Neurons try to control their gain (amplification factor) to have roughly the same range ...
  • 3,045
12 votes
Accepted

What limits the speed of human perception?

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. ...
12 votes

Why do I still see a bright light after looking directly at it?

Short answer The effect you describe is called a negative after image. It can be explained by adaptation effects of the photoreceptors in the eye. Background source: Dresden University Steadily ...
  • 51.5k
10 votes
Accepted

What is the smallest touch sensation that a human can feel?

Short answer The detection threshold of static indentation stimuli on the palm of the hand is approximately 10 to 40 micrometers, dependent on the exact location under investigation. Background The ...
  • 51.5k
10 votes

Best colour for a dog to track an object against green background

Dogs are a dichromatic species, featuring only a long wavelength (L) and a short wavelength (S) cone (source: Smithsonian). As such, they are thought to perceive mainly blues and yellowish hues (Fig. ...
  • 51.5k
9 votes
Accepted

Is brain plasticity such that we can train ourself to see with our ears?

Short answer Yes, we can see with our ears. Background Bach-y-Rita famously stated "We see with our brains, not our eyes". Bach-y-Rita worked for decades on sensory substitution. Sensory substitution ...
  • 51.5k
8 votes
Accepted

How precisely can we sense temperature differences?

Short answer Temperature differences of 0.02 degrees Celcius can be distinguished, dependent on various factors including experimental conditions and bodily location. Background The ability to ...
  • 51.5k
8 votes

Can one see flickering of a light bulb at 50 Hz?

A lamp flickers at 2x the mains frequency, i.e. 100 or 120 Hz, and that is typically not noticeable to human eyes. It is visible to chicken and insects. That being said, a low quality lamp or a lamp ...
  • 181
7 votes

Why is wind cold for humans?

This phenomena has nothing to do with any different kinds of receptors. When we are wet, we have lots of water on our surface. The evaporation of water causes cooling. Blowing wind tends to make ...
  • 1,679
7 votes

Perception of distant lights without glasses

This phenomenon is known as bokeh. You are right in the hexagonal shape being produced by the iris (of the camera), and from this, it is clear why this happens: The iris blocks out some of the light ...
  • 9,364
7 votes
Accepted

What is the science behind the inaccurate perception of colors?

To explain the neurophysiological background to the existing answers I would like to add the following: The effect you are describing (pinkish appearance of white) is generally referred to as a ...
  • 51.5k
7 votes
Accepted

Perception of white in the absence of rods

Short answer Cones mediate the perception of white in photopic conditions. Rods mediate the perception of white in scotopic conditions. The rod system is not needed for cones to mediate white ...
  • 51.5k
6 votes
Accepted

Why do I feel funny in my tummy when riding a virtual roller coaster?

Why can I feel this, when no forces are actually being applied to my stomach? Acceleration sensors are in the ears and are part of the vestibular system. The vestibular nuclei in the brain uses ...
  • 4,450
6 votes

What effect does a bat's echolocation have on other bats?

Bat echolocation is an incredible and complex process. Bats can emit two kinds of ultrasonic signals. One is a short pulse (less than 5 ms long) that sweeps a wide range of frequencies (100 Hz to 25 ...
  • 524
6 votes
Accepted

Are 2 eyes necessary for 3D vision?

It seems like you suffer from a misconception. "The left eye sees more of the left side of an object..." is not how distance perception works. Otherwise we wouldn't be able to estimate the ...
  • 411
6 votes
Accepted

How exactly does sensory substitution work?

Tot start of with your definition: Sensory substitution, when one of sensory modality changes into another sensory modality to help someone restore the ability to perceive defective sensory using a ...
  • 51.5k
5 votes

Why is wind cold for humans?

As other answers and comments have stated the reason that you feel cooler when the wind is blowing (wind chill factor often gets talked about on the news) is because evaporation is speed up by the ...
  • 3,044
5 votes

Do humans perceive temperature or heat-flux? (or both?)

This is the modified answer in response to the discussion: Facts: There are warmth and cold receptors in the body at two places: The Peripheral receptors and the Central Receptors The peripheral ...
  • 3,020
5 votes
Accepted

Do humans perceive temperature or heat-flux? (or both?)

Short answer Humans sense temperature differences. Background (Including edits based upon comments) Because the question is "Do humans perceive temperature or heat-flux?", I will answer the answer ...
  • 51.5k
5 votes
Accepted

Congenital blindness due to retinitis pigmentosa - does it exist?

I have only ever heard of one case where RP caused blindness in a newborn. Unfortunately, I am unable to release the name or any details of the patient because of privacy issues and so forth. ...
  • 1,846
5 votes

What is it called when one human eye is seeing brighter color than the other?

The phenomenon in question is anisochromatopsia, however this term is rarely used. This phenomenon is always present, however it is rarely mentioned subjectively, while objective color testing will ...
  • 5,630
5 votes
Accepted

What determines the perceived pitch (frequency) of tinnitus?

Short answer Perceived tinnitus pitch tends to resemble the frequency content of the loud sound that induced the tinnitus. Background Solid, laboratory-controlled studies to the perceived pitch of ...
  • 51.5k
5 votes
Accepted

Haidinger's brush: Is this a by-product of the eye's physics, or are there any evolutionary grounds for it?

According to the link you provided, the phenomenon Haidinger's Brush seems to be associated with the macula of the retina. The yellow color of the macula may explain the yellowness of Haidinger's ...
5 votes

Are some animals, like dogs and cats, color-blind and how do we know that?

Short answer Dichromats can discriminate colors; Color vision in animals can be tested behaviorally; Trichromatic vision is not essential for most animals, but is believed to be beneficial to ...
  • 51.5k

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