Species distinctions: Modern Homo sapiens:
Weight: varies; general: approximately 40.8 to 136.1 kg ( 90.0 to 300.0 lbs)
Length: varies; general: approximately 1.2 to 2.1 m ( 4.0 to 7.0 ft)
Gestation period: approximately 9 months, between 8 and 10 months (between 248 to 310 days )
Number of young: 1 (sometimes 2 or more)
Life-span: varies, 60 to 90 years (natural death)
Diet: varies, dependent upon environment (various plants, cows, pigs, chickens, turkeys, small and large mammals, birds and their eggs, insects, reptiles, amphibians, molluscs, squid, fish, synthesized meals/artificial foods)
Distinctive qualities: bipedal; varying colours of skin covered with fine hair; uses vocal chords and appendages to communicate; may be found on all continents

Humans at present are recognized as one of the examples of a versatile zoological specimen: they inhabit most regions of the world based upon environment; their diet is not consistent and is based upon what is available; they may be nomadic or denizen, determined by what is supplied to them in their given environment; they may be active during daylight hours or nocturnal; and their behaviour may quickly change in response to situations, as their disposition is neither constant nor simplistically determined. Their abilities of complex thought, the employment of tools, masses of complex language, and increased memory span are believed to be what distinguishes this species from all others. *

Bioelectricity: One of the most common characteristics humans share with other living organisms is the electricity found within the body: the neural system, both complex yet simple in relation to other zoological subjects, and bone structure are governed by electrical impulses that relate to the brain.

Echolocation (limitations/particular circumstances): Similarly to the dolphin and the bat, humans have been observed to acquire the ability to use echolocation to navigate, however, it is under the circumstances that the human in question is either blind or blindfolded, counterpart of a dolphin in murky, dark water or bat in total darkness. To demonstrate the processes of deriving this conclusion, conceived from bat research, see the timeline below:

1739: Diderot observed that a blind person could perceive presence and distance of objects. Theories accumulated to explain this detection: skin sensitivity to temp/pressure; pressure on tympanic membrane (vibrates sound waves in inner ear); magnetism, electricity, "sixth sense".

1893: Dresslar experiments on detection of echoes reflected from obstacle surfaces: eliminated different senses of blindfolded subjects and observed. 1^st condition: vision eliminated. 2^nd: vision, thermal, and facial pressure eliminated by covering exposed skin but not auditory meatus. Final: hearing eliminated by plugging ears but leaving face exposed, eyes covered. It was concluded there was the ability to detect due to some auditory mechanism but others disagreed with the results.

1944: Supa, Cotzin, Dallenbach: discovered stimulation of auditory system (not skin) was necessary and sufficient to detect objects. When air-waves prevented from impinging on exposed skin of blind/blindfolded, the subject could still detect obstacles by listening to footsteps. When hearing was eliminated and skin left exposed, objects could not be detected.

1947: Worchel, Dallenbach: found partially deaf and blind could not detect obstacles if hearing was prevented. If skin of external ears covered but auditory meatus exposed, obstacles could be detected. Therefore, auditory stimulation was the mechanism used to detect obstacles in blind.

1941: Griffin, Galambos: 1941, gagged bats to prevent emission of supersonic cries; plugged ears to prevent echo reception to show the increase in collision frequency.

Cotzin, Dallenbach: after showing importance of hearing, found that in order for the blind to avoid collisions with a wall, must hear changes in sound pitch with frequency above 10kHz. (Higher frequencies allow better echo resolution reflected from small targets)

1953: Ammons, Worchel, Dallenbach: blindfolded subjects able to detect obstacles outdoors, revealing that subjects relied on/sought out non-auditory clues like odors and shadows- other senses enhance obstacle detection

1962: Kellogg: blind subjects presented with two flat disks of same diameter. For each trial: a pair of targets, where one was at constant distance with the comparison at variable distance. Targets presented one after another in a pair in rapid succession. Subjects were to generate any sound desired (acoustic signals: tongue clicks, hisses, whistles, voice, the latter which was preferred by subject). Target size kept constant as distance changed: subject was to report larger of targets by listening to echoes reflected off disks. Kellogg observed that objects closer to observer thought to be larger than standard of same diameter, where objects further away were perceived as smaller.

The blind have an ability to discriminate objects of different size, with up to 100% accuracy, the smaller object of two different sized objects (placed at same distance). Performance decreased as distance increased.

1965: Rice: percent correct detection was proportional to size and distance of object from observer. At greater distance, objects needed to be larger to be detected. As object was placed further, sound intensity of echo lowered and object detection became more difficult. As object size increased, detection improved. Therefore sound intensity of echoes (size and distance manipulated) affected ability to detect.

Type of sound suitable for human echolocation also was studied: self-generated preferred sound (hisses, clicks, etc) were to be found as useful as artificial sound. All subjects moved heads from side to side in "auditory scanning" (Kellogg), which emphasizes intensity and arrival time of returning echoes at both ears, thus the blind could enhance binaural localization of sound localization of target from echoes reaching both ears.

Echolocation may be used by blind to perceive presence, dimensions, size, distance of target as size and distance affected the amplitude of echo. For example, a larger target reflects more echo energy and may be perceived as louder echo. Other factors of possible affect upon amplitude: reflective properties of material, spreading loss from distance range, and the atmosphere. Due to spherical spreading loss, a target further away reflects an echo that is observed as a weaker sound which may be perceived as smaller target or as further distance: a target placed closer to observer reflects stronger sound that may be perceived as larger size or closer distance. The pretense for placing smaller target at closer comparison distance and larger at farther distance is based on the assumption that the effects of size and target distance on the resulting echo amplitude may not be perceived separately by subjects, who found it easier to differentiate in distance between two equal-sized targets when the distance was closer to them. Changing the size of one target disrupted the blind subjects and their ability to use echolocation to differentiate in distance between targets.

The inability of blind humans to use echolocation to discriminate differences in distance when target size changed is differs from bats, who distinguish size changes from distance changes using echolocation. However, experiments have determined that blind humans are capable of employing echolocation to seek out objects in their proximity and exert more control over quality perception of local objects.

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Anemaw [Animal Electromagnetism and Waves] © Elizabeth Gerrow 2002 .