exam 1 sen/percept module 3

Sine wave

a smooth, repeating pattern of change around a midpoint

• can describe how luminance changes across space

two critical dimensions:

• 1. Amplitude describes the size of the change from the midpoint . In a visual pattern, greater amplitude produces greater contrast

2. Frequency, in vision, describes how often the pattern repeats across SPACE

• Low frequency = fewer, wider cycles

• High frequency = more, narrower cycles

Acuity

the smallest spatial detail that can be resolved

• Often measured by the visual angle of one cycle of the finest high-contrast

grating resolvable

Cycle

is one complete repetition

Grating

a pattern of alternating light and dark bars, composed of multiple cycles

• Each cycle is one pair of a light bar and a dark bar

Contrast

difference in luminance between adjacent regions

Spatial Frequency Filtering (Low & High)

number of cycles per unit of visual angle.

• Measured in Cycles per Degree.

• Low spatial frequency = fewer, wider cycles

• High spatial frequency = more, narrower cycles

mona lisa concept= filtering

Low Spatial Frequency shading around the cheeks is more smile-like

•Smile appears more pronounced when viewed peripherally or at a distance .

• High Spatial Frequency – actual details of mouth are less smile-like than shadows indicate

• Smile appears weaker when viewed with Central Vision, which works up-close in good lighting

Retinal Ganglion Cell Responses

respond to spatial frequencies based on the size of their receptive fields, which act as spatial filters for incoming visual information

• responds most strongly to a spatial frequency that matches the size of its receptive field

Retinal Ganglion Cell Phases

The phase of the sine wave is its position relative to a fixed marker; given in degrees. Measures light/receptor alignment

7 Steps of Visual Path from Optic Disk to V1

1.Optic Disk (Blind Spot)

2. Optic Nerve

3. Optic Chiasm

4. Optic Tract

5. Lateral Geniculate Nucleus

6. Optic Radiations

7. Primary Visual Cortex, aka V1 aka Striate

Lateral Geniculate Nucleus (LGN)

is in the Thalamus in each hemisphere, Relays visual signals to V1 while integrating feedback from higher cortical areas

Striate (V1) (Area 17)

• has 6 layers

• v1 is the perceptual processing

Topographic Mapping

orderly mapping of world onto retina, which is relayed to the LGN, and then forwarded to the Striate Cortex

Cortical Magnification

the brain's way of giving more processing power and space to the parts of our body or vision that need the most detail

• Causes images in the periphery to have much lower resolution than

at fixation

Fovea area processed by a larger part of V1, i.e., fovea representation is greatly magnified

Visual Clutter

he negative effect of clutter on peripheral object detection

Simple Cells

requires precise alignment with RF field

Hubel & Wiesel discovered 2 V1 cell types: Both detect bars of light or dark and support early visual processing of edges, movement, and direction.

complex cells

only orientation matters; not perfect RF position

Respond to light/dark anywhere within RF, if orientation is correct

• More flexible, often motion sensitive along a preferred axis

Columns

A vertical arrangement of striate neurons.

• Organization ensures neurons with similar tuning are grouped together (have orientation tuning within 0.5mm)

Hypercolumns

1 mm blocks of V1 neurons that process all details from a small FOV region. Includes orientation, color, and eye dominance processing units.

Interocular Transfer

transfer of adaptation from one eye to the other

infants and early childhood (birth-4 years)

Newborns have poor visual acuity and low contrast sensitivity= struggle to detect high spatial frequencies (fine details).

• Fovea is underdeveloped at birth and reaches full maturity around 4 years old.

• RGCs continue forming connections, and cones in the fovea become smaller and more densely packed, increasing acuity

Effects of visual deprivation

Monocular vision during critical period causes major cortical physiology changes, which can cause permanent spatial vision loss.

Strabismus: Eye alignment Problem aka Cross- eyed.

• Is a common cause of amblyopia

Amblyopia: A Visual Acuity Problem aka Lazy Eye

• Reduced spatial vision in an otherwise healthy eye – brain ignores it – so eye gets worse if untreated

• Anisometropia: A condition in which the two eyes

have different refractive errors.

optic disk (blind spot)

1st step - The retinal ganglion cell’s axons converge at the Optic Disk (blind spot bc no rods or cones) to form the Optic nerve

optic nerve

2nd step- The optic nerve goes to the optic chiasma where the retinal axons are separated by L & R visual field –most connect to optic tract.

optic chiasm

3rd step- At Chiasm – fibers organized by FOV; left FOV by right LGN; R FOV by L LGN

optic tract

4th step-a bundle of nerve fibers in the brain that carries visual signals from the optic chiasm to the lateral geniculate nucleu

lateral geniculate nucleus

5th-processes and routes visual information from the retina to the primary visual cortex

optic radiations

6- The Optic Radiations go to the occipital lobe’s Visual Cortex (V1) at the back of the brain.

• This is the 1st cortical stage for processing conscious info

primary visual cortex, v1, or striate

7- the first brain region that receives and processes basic visual signals from the eyes

period

is the time for one cycle,

wavelength

is the distance for one cycle

optimal responses

occur when the frequency

of the grating aligns perfectly with the center-

surround structure of the RGC.

weaker responses

occur when spatial

frequencies are too mismatched – either too

low (too broad) or too high (too narrow) for

the RGC's receptive field.

childhood to adolescence (4-10years)

Sensitivity to high spatial frequencies continues improving as V1 refines processing.

• By ~6 years old, contrast sensitivity is close to adult levels, but fine-detail sensitivity conti.; improving slightly next few years.

Peak spatial frequency sensitivity is reached around age 6-7, with only minor refinements continuing after that

adulthood and aging

Sensitivity to high SF remains stable through early adulthood,

• gradual decline begins in the 30s-40s due to aging of the optics of the eye (lens changes, reduced pupil size, etc.)

• Spatial resolution declines mainly due to optical factors, not cortical ones in middle age.

• 60s+ = significant drop in contrast sensitivity, particularly at higher spatial frequencies