Umwelt (1st part)           

Part v 
	a.  Levels of control
		1.  Receptor screening
		2. Salience and relative amplitude
		3.  Configural analysis: imposition of order	
	b. Audition & vestibular sensation
		1. Auditory/vestibular receptors
		2.  Information from vibration
			a.  Moth bat detectors 
			b.  Bullfrog mate recognition 
			c. Human speech perception 

Reading : kalat: chapt 7 (4th edition chapt 8)
		coursepack: alcock "nerve cells & behavior patterns"
For next section on vision, read kalat chapter 8 (4th ed chapt 7 plus pp 286-298)

From the philosophy of kant:  noumena    vs   phenomena  distinction
	world of phenomena = world as experienced
	world of noumena = world as actually is

This distinction highlights that what we see, perceive is a construct of our brain and mind.  We are limited to the perception of phenomena.  We do not world as it is.  Instead:
			-some stimuli not detected
			-some detected but screened out before perception
			-some enhanced/reduced/distorted
			-some actually imposed
	
Umwelt  =  perceptual world of a particular species
Extension of phenomena world by von uxekull
(kant's phenomena world= human umwelt)

What determines content of an umwelt?
3 levels of control:
1. Receptor sensory sensitivity
	- ex: are there visual receptors?; If so: colors?, Ultraviolet or infra red light?, Etc.
	- some sensory modalities are alien to humans: electric currents, voltage pulse, light polarity

2. Salience: relative noticeability
-neurally determined by relative neural processing
-consequence of labeled line processing 
(=muller's law of specific nerve energies [kalat])
	- ex 1: which modality important: human visual cortex vs sheep smell,  rodent touch
	- ex 2. Within each modality for the brain there are 'topographic map' representations
		-vision: retinotopic map - enlarged focus of attention (fovea)
		-touch: somatotopic map: hands, face (homunculus);  cetacean trunk
		-hearing: nonspatial pitch: tonotopic map

3. Organization & imposition of order: construction of percepts
- a. Simple example: depth perception: constructed from motion parallax (single eye) & retinal disparity (binocular)
- b. Moderate example: gestalt rules of perception
	- proximity  (dashed line a)
	- closure (triangle)
	- good continuation (crossed x : 2 lines, not 4)
	- similarity: color
	-common fate (movie flicker)
-c. Complex example:  perception of meaningful forms
	fledgling turkey recognition of visual predators:  
	gull chick recognition of parents:	
	human 'filling in' of  blind spot contents:
	human infant facial recognition (as imitation of expression)

B. Specific sensory modality:  hearing & vestibular sensation
Why do hearing and vestibular sensation originate from same cranial nerve?
	-originate from same evolutionary precursor:  lateral line organ
	-originate from same physiological organ: cochlea/otilith organ (semicircular canals)
Although they share a common receptor type (pressure-sensitive sensory hair cell on membrane) there are separate labeled lines for each, to separate  cranial nuclei
Therefore a quantitative receptor difference becomes a psychological qualitative difference (audition vs vestibular sensation)

Hearing and cochlea
Hair cells on basilar membrane of coiled cochlea:  tuned from high to low as membrane thickens
	apex = 100 hz to oval window = 20,000 hz
Coding of pitch mixes labeled line code (place code) with a temporal frequency code
- very low sounds (15 to 100 hz):  pure frequency
-medium pitch (100 hz to 5000 hz): combination
	-volleys :  frequency code by teams of neurons
	- place code: place on basilar membrane has maximal excitation (due to maximal wave)
-high pitch (above 5000 hz):  place coded

-brain processing of audition:  
Pitch: all cochlear codes converted to brain place codes in auditory nucleus (labeled lines)
	-tonotopic sound map in auditory nucleus, thalamus (medial geniculate) and auditory temporal cortex
Location: separate "stream" through other labeled lines to olive in medulla

Brain perception of auditory information
Three examples, from simple to complex:
I.  Bat detection by moths
	a1 auditory neuron =   gradual firing, low threshold 
		a1 elicits negative phonotaxis: servomechanism to swerve away
	a2 auditory neuron: high threshold,  all or none spike burst
		a2 elicits reflex: fold & flip
	a1 & a2 are arranged in a neural hierarchy.

Ii.  Mating call recognition by female bullfrogs
Must recognize the pattern of sound energy at particular frequencies.
	energy at 300 hz and at 1400 hz, but not in between
Stages of processing:
1. Cochlear nucleus: -tonotopic cell coding captures relative salience of frequencies
2. Inferior colliculus has three type of "recognition" neurons, arranged in hierarchy: 
	a) either/or detectors of peak frequencies
	b) inhibitory detectors for middle frequencies
	c) 'and' detectors of peaks plus middle trough =  call recognition

Iii.  Human speech perception
Syllables : natural units of perception, but don't have a 1:1 correspondence to physical units
Example: consonants sa vs ta:  no new physical unit needed for "t"
	   vowels coded by shape of multi-peak wave (energy plotted at frequencies): must analyze relative energies
Human brain can do this via a process similar to that used by the bullfrog except
	a) code recognized at level of neocortex (temporal lobe auditory cortex), not inferior  colliculus
	b) speech unit templates acquired by learning rather than innate pre-programming
	c) neural circuitry details are so complex that they are not yet understood.  Thus animal examples such as the bullfrog remain our best neural models of auditory recognition so far.

	 Sensation & perception (umwelt):  second partPart v 
C.  Vision

1.  Receptors
	a. Rods & cones
	b. Comparative color vision

2. Visual form perception by mammalian brains
	a. Receptor lateral inhibition
	b. Retina-thalamus-cortex projections
		1. Lateral geniculate (thalamus) fields
		2. Cortical: simple cells, complex cells,
			&  hypercomplex cells
		3. Pontifical cells versus visual frequency analyzers

3.  Visual perception after damage to the visual cortex:
	a.  Blindsight

4. Programming by early visual experience
	a.  Mere exposure: cataracts and "lazy eye"
	b.  Fine tuning of binocular vision and feature detectors

Visual receptors in retina
	rods (120 million) 
	 cones  (6 million - clustered primarily in fovea)
-rods are monochromatic, sensitive to 500 nanometers wavelength 
-cones come in 3 types.  Each type has its own sensitivity curve, with respective peaks at 445,  535,   570  nanometers 
-presence of multiple receptors with different wavelength sensitivities =capacity for color perception
	(example of comparision between humans, other mammals, and honeybees in class)

Shape/form perception
Shape begins to be processed in retina: lateral inhibition intensifies edges 

Lateral inhibition is also seen in center-surround receptive fields of ganglion cells

Projections to brain 
Each retina projects to both sides of the brain.  But each half of the brain receives only one half of the visual field.
	most retinal projections go to thalamus (lateral geniculate nucleus)
	each lgn layer forms a retinotopic map of contralateral visual space, and the maps are stacked on top of each other.

Brain receptive fields
Thalamic lgn neurons
	-like retinal  ganglion cells, they have a center/surround circle organization,  but are
		1. Larger  (combined) & stronger antagonisim
		2. Color coded into opponents pairs 

Cortex
Occipital cortex: area 17 - striate cortex  (medial surface in humans) 
A. Simple cells (area 17 v1)
	1. Binocular cells
	2. Bar shaped fields: responds to spot in bar
	3. Center/surround organization preserved
	4. Bar orientation organized in cortical columns: all cells in column have same orientation selectivity

B. Complex cells (in area 17  & 18; v1 and v2)
	1.  Require a full bar stimulus to activate cell; not a mere spot in bar
	2.  Sensitive to direction of stimulus movement
	3.  Some complex cells respond also to illusory contours

C. Hypercomplex cells (area 18; peristriate cortex):
	1. Length of visual bar stimulus is critical;  overlong bar inhibits firing
	2. Some cells respond selectively to visual corners (2 edge detectors combined)

-note hierarchy of coding features from thalamus cells to cortical simple, complex, and hyper complex cells.:

-further visual projections: area 18 to area 19 occipital to inferotemporal lobe
- so how do real objects become recognized?
	a. In principle, pure hierarchies could code by "pontifical" recognition
	b. But pontifical neurons are rare.  An alternative is  network processing
		1. Suggested by the separation of visual features into parallel cortical paths: shape, color, movement emphasis (separation into color blobs = anteriordorsal occipital v4 cortex, detail interblobs to inferior temporal cortex, and movement magnocellular= middle temporal at area 17 v1)
		2. Shape recognition may be similar to "reverse fourier analysis"
			complex cortical cells respond to sine wave gradients even better than bars
		3. Recent finding: cross cell synchrony of firing when features are part of the same object.  This supports a network pattern code

Extra-striate visual perception
-parallel projection path from retina to superior colliculus    (then to thalamus pulvinar, temporal cortex etc)
	may code:
	1.  Position in space, eye movements, attention
	2.  Possibly even 'nonconscious' perception of shape 
		-blindsight after area 17 lesion

Infant development and early visual experience
Evidence for "tuning" of visual neurons by psychological experience
1. Human cataract 
	adult correction of cornea does not restore form perception if condition existed at birth 
2.amblyopia (lazy eye): eyepatch therapy reduces acuity of "good" eye
3. Strabismus (cross-eye, wall-eye):  no binocular cells unless corrected in infancy
4.  Feature recognition programing by experience: direction of bar orientation for simple cells depends upon orientation seen in infancy.