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 ...


43

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 evolved as a way to decrease the risk of ingesting toxic substances, which may explain why many drugs taste bitter. In other words, classes of compounds that may harm ...


36

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

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: [...] ...


20

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 ...


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

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

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

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

Short answer Optical filters can optimize color contrast, but never restore color blindness. Filters remove colors, they can never add something. 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 ...


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

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 discriminate temperature differences depends on whether it is a cooling or heating pulse, the skin temperature, the duration of the temperature stimulus, age, bodily ...


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

"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... ...


7

Short answer Frogs are nearsighted on land and farsighted under water. Background Frogs are reported to be nearsighted on land, but farsighted underwater (source: Chegg Study). Nearsightedness (myopia) is a condition in which near objects are perceived clearly, but objects farther away are blurry. Farsightedness (hyperopia) is the reverse. The human ...


7

Humans' poor sense of smell is a myth, borne of 19th century speculation rather than actual data. This is described in an excellent recent paper in Science , "Poor human olfaction is a 19th-century myth" by John P. McGann. Quoting from a recent blog post of mine, The myth dates to the work of the pioneering and hugely influential anatomist and ...


6

Short answer Proprioceptic receptors provide a feedback mechanism from the body to the brain, telling the brain what our limbs are doing and where they are with respect to the body without visual feedback being needed. Background Muscles, skin and joints contain proprioceptic receptors. They sense position and movement of our limbs and trunk, they register ...


6

@bshane has already provided an excellent answer to the question. However, I just found a recent review published in Molecular Ecology (Winternitz et al., 2016) in which the authors performed a phylogenetically controlled meta-analysis on MHC-dependent patterns of mate selection in humans and non-human primates. They used studies from seven primate species ...


6

The frequency tuning in the cochlea is due to a number of factors. The primary factors of cochlear frequency tuning are generally ascribed to the passive physical characteristics of the basilar membrane (BM), which OP already identified in the question - The BM is wider and more flexible at the apical end (low-frequency region) and narrower and stiffer at ...


6

There are several factors in human. we are upright, which brings the nose just about as far away for scents as it can get, you want your nose as close to the ground as possible for the most efficient use scent. This is not in and of itself a deal breaker but it is an important factor which made smell less important for us. Our large brain is competing for ...


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