The Visual System:Feature Detection

ModelLesson 17

Cortical Mechanisms

Primary Visual Cortex - V1 Striate or calcarine cortex

Hubel and Wiesel - Nobel Prize Single cell recording

Feature detection model simple stimuli complex perceptions ~

Feature Detection Model

Visual perception of objects detection of simple features points, lines, corners, curves

Convergence of information retina LGN V1

Primary Visual Cortex (V1) Simple cells complex cells hypercomplex cells ~

Simple Cells Detect lines & edges

not center-surround Best stimulus

bar of light or line particular orientation particular location ~

Simple Cells

LGN neurons RF center-surround converge onto simple cells (V1)

Bar of light APs in simple cell ~

Simple Cell

Simple Cells

wrong location or angle doesn’t affect simple cell ~

LGN

V1

Wronglocation

Wrongangle

Complex Cells

In V1 & V2 (secondary visual cortex) Convergence

of LGN & simple cells responds to movement

Best stimulus line or bar Fixed angular orientation Location not as important preferred direction of movement ~

S1 S2 S3

Complex Cell

Complex Cells

V1

V1/V2

Hypercomplex Cells

V1 & V2 Complex cells converge Hypercomplex cells

Best stimulus lines of specific length Detect Corners ~

Feature Detection Theory Features = lines & corners

Can it represent a curve?