PSY605: Perception

No -- influenced by top-down processes

Higher order processes influencing sensations

• Converting stimulus energy to neuronal firing
• Accomplished by sensory receptors

• Exteroreceptors - stimulus on body: skin, tongue
• Telereceptors - Distant stimulus (vision, audition, smell)
• Proproioceptors - muscles, joints, vestibular system
• Interoceptors - Internal organs

• Modality (what) - Type of receptor activated
• Position (where) - Location of receptors and pattern/frequency of firing (audition, smell)
• Intensity (how much) - # of neurons firing and frequency of activity (audition, smell)
• Timing (when) - onset of firing

• 1. Sensory receptors are optimized to detect different stimuli
• 2. Sensory info is carried along labeled (specified) lines - as long as these neurons are activated, we'll have that perception
• 3. Center-surround organization
• 4. Decussation (crossing) of sensory fibers
• 5. Topographic representation (but distorted) - homunculus

• Center - excitatory
• Surround - inhibitatory

Adds precision

50%

380 to 760 nanometers

• Subset of retina corresponding to center of visual field
• Has no rods, only cones

• Part of visual scene corresponding to where the optic nerve leaves
• No visual receptors

• Cones
• - Color
• - Found more in fovea

• Rods
• - Brightness
• - Found in periphery of retina (none in fovea)
• - Important at night

• Photoreceptors (rods and cones)
• Bipolar Cells
• Ganglion Cells - (1 million) axos form the optic nerve and exit at the optic disc (which forms the blind spot on the retina)

• Optic Nerve
• Optic Chiasm - where part of optic nerve crosses over
• Optic Tract - Portion after chiasm
• LGN in Thalamus - first point of synapse; relay of visual information
• Radiations - Portion after LGN
• Primary Visual Cortex (V1), Visual Cortex
• Parietal lobe (where/how) and Temporal lobe (what)

• Temporal Hemiretina
• - Contralateral hemifield's medial portion
• - Stays on same side

• Nasal Hemiretina
• - Ipsilateral hemifield's lateral portion

• No input from left eye
• Left and right visual field in right eye

Only see right field in left eye and left field in right eye

Both eyes see only see left visual field

• Donut shaped
• Organization in LGN
• Turns into columnar organization in V1

Organization in V1

The area of the retina that, when stimulated with light, changes the cell's membrane potential

• Captures every point in the visual field and maps it onto the retina, V1, etc.
• Represented in 360 degrees
• Neighboring cells in the retina feed information to neighboring places in their target structures (i.e. they "stay neighbors" in LGN, V1, etc.)

Receptive field - what part of the visual field does a neuron respond to?

Selectivity - what kind of visual information does the neuron respond to?

Different kinds of visual information are processed in parallel by different neural populations

Hubel and Wiesel (Nobel Prize 1981)

• V1 - Orientation
• V4 - Color
• V5 - Motion

• Cytoarchitecture
• Intracortical connections
• Retinotopy
• Functional properties

• From optic nerve cells --> Superior colliculus (midbrain) --> Pulvinar (thalamus) --> Temporal lobe ("what") and Parietal lobe ("where/how")
• "Rough and ready" vision
• Responsible for "blindsight" when main pathway is damaged

• Olfaction
• Instead goes to Olfactory Bulb

Chemical senses

Axons from nasal receptors clumping together in olfactor bulb, form olfactory nerve

Primary olfactort cortex and secondary olfactory area (orbitofrontal cortex)

• Hard to get signal in fMRI
• Passive smelling vs. active sniffing
• Massive amount of habituation in smell

• Smaller nostril (low air flow):
• -Odorant with high rate of absorption = small neuronal response
• -Odorant with low rate of absorption = large neuronal response

• Larger nostril (high air flow):
• -Odorant with high rate of absorption = large neuronal response
• -Odorant with low rate of absorption = small neuronal response

Close proximity from oldactory buld to hippocampus and amygdala

• No distinct topographic representation in CNS
• Model 1: Taste receptor-specific signaling pathway defines perception (in PNS)
• Model 2: Taste neuron projection defines perception (in CNS)

Umami - all over

• Cochlea - Basilar membrane
• Inner ear fluid moves hair cells

• Primary recepters (hair cells in the cochlea: Organ of Corti)
• Intermediate-level relays (MGN of thalamus and inferior colliculus in brainstem)
• Primary cortical representation (auditory cortex in temporal lobe)
• Higher integrative areas

Compared to most mammals, humans' sense of smell is poor.

Auditory mapping system - frequency (pitch)

Thick blood cells

The eyes are constantly moving so we never actually see our blind spot