78

There are about 100 (Purves, 2001) to 400 (Zozulya et al., 2001) functional olfactory receptors in man. While the total tally of olfactory receptor genes exceeds 1000, more than half of them are inactive pseudogenes. The combined activity of the expressed functional receptors accounts for the number of distinct odors that can be discriminated by the human ...


34

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 types of color photoreceptors, called cones. They are sensitive to red, green and blue, respectively. Colors are processed in the retina through a process ...


33

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 temporal limits of our visual system, it is unlikely to be perceivable. Background The temporal resolution of the visual system can be quantified in a ...


28

Short answer Yes, taste sensations can be generated electrically. However, we cannot taste electrons themselves, as taste-receptor proteins on the taste receptor cells are not activated by electrons. Instead, electrical currents stimulate taste receptors directly by depolarizing the cell membrane, without the need of activation of the proteins that normally ...


21

Cats and dogs can both view tv screens & monitors ... though their viewing experience is a little different to ours thanks to differences in cone structure leaving them color blind and giving low acuity. Both species have lower levels of color vision than humans. Cats see slightly more color (in the blue green and yellow end of the spectrum) than dogs ...


21

First, let's consider the original Wedekind et al (1995) study. Sample sizes seem reasonable, if the effect is not very noisy: [...] 49 female students (average age: 25.2 years, s.d. = ­4.0) and 44 male students (average age: 24.7 years, s.d. = 2.6) [...] ... and the statistical design accounts for individual differences in a fairly robust way: [...] ...


19

First of all, great question! What you describe here is known as aposematism. Aposematism is the adapation of warning signals against the predator. This word is used for any sound, coloring, and odor used as a warning signal. Of course, for this question the focus is color. Honest indications Animal coloration is usually an honest indication of their ...


17

In short, it's because your brain processes external and self-produced stimuli differently. If someone tickles you, you feel that ticklish feeling, but when trying to tickle yourself, there is a reduction in the sensation. When you are tickled by someone, a part of your brain activates causing you to laugh, etc., but it seems that when you trying tickling ...


16

A quick diagram to point out to people who may not know what Eustachian tubes are (#2). In order for the aromatic molecule to reach the olfactory bulb, it would first have to get through the Tympanic Membrane (#22) [a.k.a. - Eardrum]. The Tympanic Membrane is water/airtight unless pierced. So, while it's plausible that an aromatic molecule could travel ...


15

There are only three kinds of optical receptors in the eye, but more than 900 kinds of olfactory receptors. Thus you can encode pictures with the three primary colors, but there is no small set of primary scents. To transmit a smell via "primary scents", you'd have to create an artificial nose that monitors the response of each of the olfactory receptors, ...


12

Preamble & Overview. This is a rather unsatisfying answer I'm afraid. I can't seem to find any animal that has exceptional eyesight and sees in monochrome. Baring in mind the context of humans vs machines; machines cope better with shapes rather than colours however it generally appears that those animals which rely on exceptional eyesight to survive ...


12

Short answer In terms of visual function, the low-tier primary visual cortex and high-tier frontal cortex are inactivated. The activity of the intermediate ventral stream and limbic regions are increased, apparently uncoupling low- and high-level vision processing from the system. Background The sleep stage where visualizations (dreaming) occur is called ...


12

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 fixate on the black lightbulb for thirty seconds or more and then immediately turn your gaze to the white region on the right. The illusionary glowing white bulb ...


11

Shampoo contains surfactants, chemicals which cause lipids to emulsify. The cell membrane is composed primarily of phospholipids, which are vulnerable to action by surfactants. In fact, sodium dodecyl sulphate (SDS, often labelled SLS on shampoo bottles), an integral component of many shampoos is also used in the lab (albeit at substantially higher ...


10

First of all one should tell that one can attribute the activation of certain brain zones with some indepent events only when the activation takes place along the signal input (receptors, sensory pathways towards the cortex and the sensory areas in cortex) or motor action (=output) (along the motox cortex => motor neuron => target organ). Those zones in ...


10

To quote the University of Sidney site: People often think that other people are staring at them even when they aren't research led by the University of Sydney has found. When in doubt, the human brain is more likely to tell its owner that they're under the gaze of another person, researchers from the University of Sydney and The Vision Centre ...


10

Ants follow odor cues in the wind. A study by Wolf and Wehner (2000) manipulated ant antennae and wind direction to show that ants followed odor plumes on the wind. A more recent study by Buehlmann et al. (2014) showed that desert ants of the genus Cataglyphis cued in on linoleic acid, a so-called necromone (death scent) released by dying insects. Here's a ...


10

Short answer Butterflies can see behind them. Background Merry et al. (2006) have estimated the field of view of the butterfly, by investigating the Orange Sulphur butterfly (Colias eurytheme): Colias eurytheme. Source: Massachusetts Butterfly Club The authors found that this butterfly has a very large visual field, encompassing 93% of the spherical ...


10

Electrical currents stimulate neurons aspecifically. For example, the BrainPort artificial vision device conveys visual information through electrical stimulation of mechanoreceptors in the tongue. Similarly, cochlear implants and retinal implants convey acoustic and visual information through electrical stimulation of the inner ear and retina, respectively. ...


10

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 sensitivity of a sensory system can be expressed as the detection threshold. This threshold is in psychophysics generally defined as that stimulus level where, ...


9

Not all cat predatory behavior is innate. Researchers found that cats predatory behavior for birds vs. mice depends to a significant degree on training by the mother: if the mother taught predatory behavior with birds, the kittens grew up to be better at catching birds than at catching mice and vice versa. Supportive data shows that aside from monkeys and ...


9

There are many, many more parameters than 200! As an example, look at the nomenclature system for olfactory receptors (ORnXm). "OR" is the root name (Olfactory Receptor superfamily) n = an integer representing a family (e.g., 1-56) whose members have greater than 40% sequence identity, X = a single letter (A, B, C, ...) denoting a subfamily (>60% sequence ...


8

In expansion to biocs' excellent answer, I would like to highlight some practical limitations of this. Suppose we did manage to create a huge database of exact chemical mixtures which produce all smells recognisable by humans. You would still meet some complications: The output device (analogous to headphones or screen) would either need to be able to ...


8

In this instance, I would say your attention has been adjusted, not your ear's ability to perceive sound. Our ears don't have a control setting or a means of adjusting incoming sound levels (though I'm certain when an ambulance with loud siren drives by, we all wish we did). What you are experiencing is a prioritization of the sound by your brain in ...


8

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 at end-of-life may also flicker at 50 or 60 Hz, and you will notice. It depends on the brightness, so an area illuminated by the lamp may not seem to flicker. ...


7

Earwax, also called cerumen, is slightly acidic (1), with a pH of about 6, and acidic foods or substances taste sour. The composition of earwax, upon which its taste depends, is related to its functions. Earwax aids in cleaning and lubrication of the ear canal and has an antimicrobial effect. The antimicrobial effect is in part attributed to its acidity, ...


7

The phenomenon you are referring to is color constancy: The apparent hue of a reflective surface remains constant even when changes in the spectral power distribution of the illuminant alter the wavelengths reflected from it (Mather, 2008). In other words, despite substantial changes in illumination, we usually experience the color of an object as being ...


7

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 perception and vice versa. Background Cones code for red, green and blue. The remaining colors, as you rightfully state in the question, can be generated by mixing ...


7

Short answer Optical filters can optimize color contrast, but never restore color blindness. Filters remove colors, they can never add anything. However, glasses like this can prove helpful for certain sub-populations of people that are partially color blind. Background First, the term color blindness is deceptive. It is better to talk about colour vision ...


7

"Rewiring" the brain isn't quite that simple: simply splicing a nerve to another doesn't necessarily mean the axons of that nerve will then grow into area. I am unaware of any studies that cross these specific pathways but as I am writing this answer I see you have already updated your question to ask about other modalities! So, with that in mind... ...


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