Through the eyes of an animal: how animals see

Ishara Mills-Henry, Ph.D.

Science of the Eye Program

MIT

ÈÈÈÈ

What do animals see?

What do animals see?

The Retina

From www.howstuffworks.com

Retina

Retina

Humans are considered trichromats

Blue, Red, and Green Cone Photorecpetors

Rod photoreceptors – are important for vision in dim light

Rods – Low light Cones – Color vision

Three Main Parts:a. Outer Segments

b. Cell bodyc. Synaptic terminal

Visual Responses• Optokinetic Response/Reflex

– Maintain image on retina stable

– Innate reflex

• Optomotor Response/Reflex– Locomotive behavior

– Hypothesized to play a role in control of speed and direction of body movement

– Innate reflex

• Escape or Avoidance Response– Avert danger

– Innate reflex

Ability to test: Colors, Spatial frequency, and Motion detection

Observing our eye movements

• Umbrellas

• Groups of three

One person twists an umbrella

while the other tries to focus on

the umbrella without moving

their eyes.

The third person can observe.

The umbrella should have a pattern or make stripes on a solid color umbrella with tape

Eye movements (microsaccades)

http://www.michaelbach.de/ot/mot_eyeJitter/index.html from Pinna B & Spillmann L (2002) A new illusion of floating motion in depth. Perception 31:1501–1502.

Involuntary eye movements – This illusion makes us aware of the small movements our eyes make. Our eyes these movements even if we think we are focusing on an object. This is to prevent the photoreceptors in the retina from desensitizing. If photoreceptors desensitize they will no longer pass the signal to the brain of the object we are seeing. It would reduce the visibility of an object.

• Drum lined with black and white stripes

• Light source illuminates drum

Optokinetic Response

Vertebrates exhibit numerous reflex behaviors that are driven by visual stimuli. The OKR response encompasses smooth eye rotations which track moving patterns followed by sharp movements called saccades.

Optomotor Response

• Zebrafish (http://baierlab.ucsf.edu/omr.html)

Escape or Avoidance Response

Compound Eyes

• From http://universe-review.ca/R10-33-anatomy.htm

• Repetitive facets called ommatidia

• Image formation probably more of a mosaic than individual images

•(But the glasses are still fun)

House crickets (Acheta domesticus)

• Omnivorous scavengers

• Feed on organic materials, as well as decaying plant material, fungi, and some seedling plants

• Active mostly at night

• Have UV (332 nm), blue (445 nm), and green (515 nm)

• Habitat: Forest and grasslands

• See polarized light (navigation purposes)

• Detect visual cues for place memory

Phototaxis

• Movement towards or away from light

Drosophila

Habitat: rotting fruit

Phototaxis

Eight photoreceptors arranged in a pattern

Vision: myopic/poor spatial quality but able to detect movement quicklySmaller lenses captures less light

Mealworms/Darkling Beetles (tenebrio moliter)

• Over 20,000 species

• Larval stages are used as a food source fish, reptiles, and birds.

• Adult darkling beetles – active both day and night

• Habitat: burrows in grain

• Eat mostly vegetation – fresh and decaying

• Spectral response – 520 nm and 334 – 365 nm (UV)

Do they exhibit negative or positive phototaxis? Does the larval stage behavior differ from the adult stage?

Planaria (Schmidtea mediterranea)

• Flatworms • Usually used to study

regeneration• Habitat: Under rocks in river beds• Eye contains pigment and

photoreceptor cells

Emperor Scorpions (Pandinus imperator)

• Found in the tropical forests and savannas of Africa

• Docile, although can become territorial and cannibalistic

• Nocturnal –hunts for prey at night

• Habitat: under rocks, logs, and other forest debris

Scorpion Fluorescence• Scorpions fluorescence under

UV light.

• Exoskeleton contains compounds that exhibit flourescence

• Recent studies suggested its for detection and avoidance of the UV light.

• Ability to discriminate between species?

• Mating, navigation, ?)

More Interesting Information

Flight Simulator for flies?

May yield info for Robot Vision

http://www.youtube.com/watch?v=e5uPr_3SsHA&feature=player_embedded

What can animals with compound eyes teach us?

Better Cameras and motion detection systems?

Measuring Responses

• Place electrode on eye

• Light stimulus flashes over the eye

Responses

Ganglion Cell Spike Recordings

a = Hyperpolarization of photoreceptors

b = On- Bipolar cells depolarization

d = OFF-Bipolar cellsdepolarization