1 7 3 Sensory Systems Active Sensing BIO 361T Fall 2014 Echolocation 1 Changes in blood oxygen level in the brain functional magnetic resonance imaging fMRI are often used as a proxy for which neurons are being used at that moment Patients will be provided with stimuli while their brains are being imaged to see how blood flow changes in response fMRI studies comparing sighted and blind individuals listening to echolocation clicks and echoes show no difference in the temporal lobe but greater activity in the occipital lobe of blind individuals Why do you think this is Temporal lobe is location of auditory cortex Both groups heard the clicks Occipital lobe is location of visual cortex which was not activated in sighted people but was activated by echolocation clicks and echoes in blind people This sensory input has taken over the deafferented visual areas 2 How does an echolocator interpret a delay between the sound it emits and the echo that returns Distance to the object 3 What kind of sound is most useful for this kind of data and why FM sweep because it is short and latency can be measured regardless of frequency 4 How does an echolocator determine how fast it is approaching a moving target The frequency shift of the echo due to Doppler effect 5 What kind of sound is most useful for this kind of data and why CF pulse because it is longer and at a single frequency 6 The outer layer of the mammalian brain the cerebral cortex includes areas for sensory input from the eyes skin and ears among others These are called the visual cortex somatosensory cortex and auditory cortex respectively The neurons of the first two are laid out in maps that correspond spatially to the animal s visual field and body surface a How are the neurons in the auditory cortex of non echolocating mammals arranged Tonotopically just like the hair cells in the cochlea recall from mechanoreception lesson b Hypothesize in what way the organization of the auditory cortex in echolocating mammals is different Explain any similarities and differences between this and the organization of the visual and somatosensory cortices Must be 2 dimensional not just linear like a map Similar in that it will correspond to spatial map but different in that it does not correspond directly to the ear like eye visual field and skin body surface The brain must perform computations comparing one ear to the other and create a map 2 7 Bats emit sounds that are 30 1 000x longer than that of toothed whales all else being equal these waves correspond to much more energy upon emission Why do you think this is necessary Air impedes wave travel more than water so signal must have more energy to travel to object and return The only energy in the waves of active sensing is what the animal puts into it 8 The chirps and clicks of bats and toothed whales are around the same frequency 10 200 kHz a Is this what you would expect Why or why not They detect smaller prey and move more quickly so one might expect bats to have higher frequency calls as higher frequency provides greater resolution b Why do you think whales can detect prey up to 50 m away while bats are limited to about 10 m With same frequency waves travel much farther in water than air 9 The echolocation calls of shrews are FM low amplitude sounds Compare this to the sounds that bats make to hypothesize as to the function of echolocation in shrews Bats make CF and FM sounds which give them detailed information about distance and movement with high resolution Shrews do not get movement information and less distance information They just use this to navigate their environment which supplements their poor eyesight Electrolocation 10 You place a rock beside an actively electrolocating fish and it learns to navigate around it If you put the fish in the same starting position and move the rock farther away how does this change the distortion of its electric field In other words how can the fish tell that the rock is farther away width of electric shadow on body near anterior end corresponds to distance 11 Why will an object that is more conductive than water create a concentrated spot in the electric field that returns to the fish an electrical bright spot The lines of current will follow the path of least resistance which will be through the cube more instead of through the surrounding water 12 Why will an object that is more resistive than water create a gap in the electric field that returns to the fish an electrical shadow The lines of current will follow the path of least resistance which will be through the water around the cube 3 13 The following graph shows the electrical image of six objects a metal cube at 12 17 or 22 mm away from the fish and a plastic cube at 12 17 or 22 mm away The y axis shows amplitude of the electric signal that the fish emits with 1 0 being no change Label each line correctly Inflection metal 22 17 12 from top to bottom Deflection plastic 12 17 22 from top to bottom Conductive objects metal cube will concentrate the lines of the electric field causing a peak in amplitude on the fish s body that corresponds to the location of the cube Resistive objects plastic cube will block the electric field causing a drop in amplitude on the fish s body that corresponds to the location of the cube There will be a difference in amplitude between the center and periphery of the shadow the center will either concentrate or block the signal the most depending on whether the object is conductive or resistive respectively The difference levels off as the item gets farther away The fish uses the size amplitude ratio to determine distance to the object Material is encoded in the change in amplitude Distance size is encoded in shape and amplitude Electrocommunication 14 In fish that fire waves of electric current as opposed to pulses each species has its own wavelength as shown in the graph below The tuberous electroreceptors of each species are tuned so that they are most sensitive to their own wavelength Match the following graphs of electroreceptor threshold to the correct species 1 2 or 3 1 3 2 15 If two pulse gymnotids genus Apteronotus brown knife fish with similar electric organ discharge EOD frequencies get close to each other the one with the higher EOD will increase its frequency farther known as the jamming avoidance response JAR Why do you think the JAR has been positively selected for Would detect other animal s electric field plus its own which would interfere with
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