sensory modalities

What are the characteristics of color vision in different animals?

- Most mammals are dichromats (lack M-cone)

- Humans and some primates are trichromats

- Marine mammals are monochromats (only L-cone)

- Color vision deficiencies:

- 5-8% males, 0.5% females affected

- X-chromosome linked (M and L genes)

- S gene on chromosome 7

How does color vision work?

Three types of cones:

- S-cones (short wavelength)

- M-cones (medium wavelength)

- L-cones (long wavelength)

Color is:

- Not physical reality

- Subjective experience from neural activity

- Result of wavelength processing in retina and brain

What are the parallel visual pathways?

P-ganglion cells:

- Small receptive fields

- Slower conduction

- High acuity

- Color-sensitive

M-ganglion cells:

- Large receptive fields

- Higher conduction speed

- Motion sensitive

- Low acuity

- No color discrimination

How does hearing work?

Sound characteristics:

- Frequency (Hz)

- perceived as pitch

- Amplitude - perceived as loudness

- Phase and waveform

- Can propagate through air or bone

Functions:

- Detect sound source location

- Spatial orientation

- Echolocation (in some species)

- Communication

How is sound processed in the ear?

Process:

1. Sound waves hit tympanum

2. Middle ear bones vibrate

3. Vibrations amplified

4. Transmitted to cochlea

5. Hair cells respond to specific frequencies

6. Tonotopic mapping along basilar membrane

How do hair cells work?

Mechanism:

1. Stereocilia bend

2. Ion channels open (K+ and Ca2+)

3. Cell depolarizes

4. Voltage-gated Ca2+ channels open

5. Neurotransmitter release

6. Excites auditory interneurons

What is the auditory pathway?

- Cochlea → cochlear nerve → cochlear nuclei

- Most projections go to contralateral cortex

- Superior olivary nuclei process binaural information

- Further processing in:

- Inferior colliculi

- Medial geniculate nuclei

- Primary auditory cortex

What is cross-modal plasticity?

- Brain areas can adapt to process different sensory inputs

- Occurs following sensory loss

- Similar coding principles across different modalities

- Allows for compensation in sensory processing

How do sensory systems interact?

Multisensory interactions occur in:

- Association cortices

- Primary sensory cortices

- Higher sensory cortices

- Superior colliculus

- Thalamus

Benefits:

- Reduces ambiguity

- Improves object detection

- Guides attention

What is the cocktail party effect?

- Ability to focus attention on specific stimulus

- Filters out background noise

- Helps in noisy environments

- Example of multimodal integration

- Demonstrates selective attention