Perception of motion depth and form
This presentation is the property of its rightful owner.
Sponsored Links
1 / 34

Perception of Motion, Depth and Form PowerPoint PPT Presentation


  • 92 Views
  • Uploaded on
  • Presentation posted in: General

Perception of Motion, Depth and Form. David M. Waitzman, M.D., Ph.D. Discussion Question. Motion in Depth lecture points:

Download Presentation

Perception of Motion, Depth and Form

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Perception of motion depth and form

Perception of Motion, Depth and Form

David M. Waitzman, M.D., Ph.D.


Discussion question

Discussion Question

  • Motion in Depth lecture points:

    • What are the two visual streams and what kinds of tasks are common to both. What tasks are different?  If an object is moving toward you what portion of the hemisphere would be activated? What portion of the cortex would recognize the object?

    • Dorsal and Ventral

    • Common: Disparity Cells in visual (V1, V2, V4) AND extrastriate (MT) cortex respond to targets closer (orange) or further (blue) than fixation point (green)

    • Different: Motion versus Object recognition

    • Near: MST (looming objects)

    • Recognition: Area IT


Phi or beta phenomenon

Phi or Beta Phenomenon

The POINT of this Demonstration: The brain is wired to perceive motion even though in this demonstration none of the objects were actually moving


Perceived motion analysis of motion occurs in a separate pathway

Perceived Motion: Analysis of Motion Occurs in a Separate Pathway

Movement of an image on the retina or an eye movement (above)

True movement or apparent (flashed) movement (right)


Receptive fields in the retina

Receptive Fields in the Retina

  • Two types of ganglion cells:

    • on and off dependent upon the bipolar neurons

  • Center Surround structure of the receptive field described by Kuffler

  • Best activated by central illumination

  • Best inhibited by annular illumination


Different view of center surround organization parallel pathways

Different View of Center-Surround Organization: Parallel Pathways

  • Transformation of visual information is evident in the ganglion cells of the retina

  • X cells – sustained linear responses

  • Y cells – transient, excitatory non-linear responses


P and m projections to lgn different physiologic channels

P and M Projections to LGN: Different Physiologic Channels

  • P cells in the retina (also known as midget ganglion cells) project to the parvocellular layers (3-6) of LGN

  • M cells in the retina (also known as parasol cells) project to the magnocellular (ventral most) layers (1-2) of the LGN

  • Intercalated layers are termed koniocellular (dustlike or tiny cells)


Comparison of p and m pathways

Comparison of P and M Pathways

  • P  Parvocellular

    • Small Receptive Fields

    • Slow conduction to LGN

    • Sustained responses (X Like)

    • Sensitive to color

    • High contrast

  • M  Magnocellular

    • Larger receptive fields

    • Rapid conduction to LGN

    • Transient responses (Y like)

    • Broadband color sensitivity

    • Low Contrast


Anatomic segregation of motion and object recognition pathways

Anatomic Segregation of Motion and Object Recognition Pathways

  • parvocellular: 4C“high acuity”; to blobs; to thin stripes, to V4 (color)

  • magnocellular: 4Ca “motion pathway”; to layer 4B of V1 and to V2 (area 18) and hence to Area MT


Mt solves the aperture problem

MT Solves the Aperture Problem

Top : Grating moving in any of 3 apertures has the same apparent

motion

Bottom: In MT two edge detecting neurons are linked to

permit identification of the overall motion of the entire object


Plaid motion v1 versus area mt

Plaid Motion: V1 versus Area MT

Neurons in V1 encode the direction of individual components of motion (top)

MT neurons encode the perceived speed and direction of the moving visual stimulus (below)


Confirmation of different pathways from clinical syndromes

Confirmation of Different Pathways from Clinical Syndromes

Type of Agnosia

Symptoms

Can’t name use or recognize real objects

Doesn’t recognize drawn objects

Can’t recognize faces

Doesn’t associate a color with an object

Can’t name colors

Can’t distinguish hues

Loss of stereoscopic vision

Can’t see objects moving

  • Object agnosia

  • Agnosia for drawings

  • Prosopagnosia

  • Color Agnosia

  • Color anomia

  • Achromatopsia

  • Visual spatial agnosia

  • Movement agnosia


Dorsal and ventral streams

Dorsal and Ventral Streams

  • Dorsal Stream: Where: Motion

  • MT projects to MST

  • MST projects to inferior parietal

  • lobule 7a and to the FEF

  • Ventral Stream: What : Form and Color


Smooth pursuit characteristics

Smooth Pursuit: Characteristics

Purpose: Track visual stimuli moving at < 100/s

Stimulus: Step-Ramp


Smooth pursuit characteristics1

Smooth Pursuit: Characteristics

Despite a target appearance on the contralateral side, initial pursuit velocity is in the direction of smooth motion


Area mt physiology

Area MT Physiology

  • MT neurons encode visual stimulus motion (discharge is reduced when target is blanked)


Mt lesion scotoma for motion

MT Lesion: Scotoma for Motion

  • Scotoma (i.e., blindness) for motion in a specific portion of the contralateral visual hemifield.

  • Saccades to moving targets in the blind area are inaccurate, e.g., note the overshoot of the leftward saccade at down arrow

  • Monkeys cannot estimate the speed of the target until it is outside the “motion blind” area

  • Saccades to stationary targets are normometric


Area mst perception of eye motion

Area MST: Perception of Eye Motion

  • Neurons in area MST receive a signal of current eye and head velocity (A)

  • large visual fields

  • can estimate heading and target motion by eliminating self motion

  • Discharge not reduced when visual stimulus is blanked or stabilized (B)


Mst lesions loss of eye speed toward the ipsilateral side

MST Lesions: Loss of Eye Speed Toward the Ipsilateral Side

Two deficits:

  • retinotopic deficit: cannot estimate speed in a region of contralateral visual hemifield

  • unidirectional loss of smooth pursuit toward the side of the lesion REGARDLESS of which visual hemifield the stimulus is presented


Monocular cues for depth perception

Monocular Cues for Depth Perception

  • Familiar Size

  • Occlusion

  • Linear perspective

  • Size perspective

  • Distribution of shadows and illumination

  • Motion Parallax

  • And…..


Binocular cues for depth perception disparity tuning

Binocular Cues for Depth Perception: Disparity Tuning

A binocular disparity signal arises in V1 (Hubel and Wiesel)

Cells in visual (V1, V2, V4) AND extrastriate (MT) cortex respond to targets closer (orange) or further (blue) than fixation point (green)

Both dorsal and ventral pathways have disparity tuning


Dorsal pathway area mt direction and disparity tuning

Dorsal Pathway (Area MT): Direction and Disparity Tuning

Tuning for targets closer or further from the monkey (near and far response patches)

Newsome et al, J. Neurosci. 1999


Ventral pathway v4 binocular disparity

Ventral Pathway (V4): Binocular Disparity

  • Tuning in depth

  • Dorsal and Ventral Streams NOT Segregated for Disparity (a common feature)


Color and form are major differences in ventral path

Color and Form Are Major Differences in Ventral Path

  • Human subjects undergo PET scan to demonstrate motion regions (left column) and color regions (right column) corresponding with monkey area MT and V4 respectively


Illusory contours in v2 neurons

Illusory Contours in V2 Neurons

  • Receptive field of the neuron is the ellipse

  • Strong activation when an edge passes over the receptive field

  • Persistent activation when an illusory contour passes over receptive field (2)

  • No response when the edge is partial (3 and 4)


V4 neurons sense gaze position not movement and relative size

V4 Neurons Sense Gaze position (not movement) and Relative Size

  • View objects at 3 different distances and at 9 different gaze positions


Perception of motion depth and form

  • Spike rasters of the stimulus (S) period for each of the 27 experimental conditions

  • The center figure represents the mean firing rates for this cell during both the fixation period (FO, blue bars) and the stimulation period (S, red bars)

  • Leftmost graphs show the mean firing rate data during the stimulation period using an interpolated color plot. Each of the planes represents a monitor viewing distance.


V4 neurons complex forms size orientation color but not faces

V4 Neurons: Complex forms, size, orientation, color, but not Faces

  • On the right, contour plot of the S (size) regions (WHITE) is superimposed on a color-coded map of orientation preference. Color saturation within this map indicates orientation selectivity. Unlike in V2, S regions in V4 are not limited to unoriented regions, but can span iso-orientation domains.


Inferotemporal cortex respond to form color and faces

Inferotemporal cortex respond to form, color, and faces

Cells increase in complexity of object recognition, but lose the ability to spatially localize objects (no gaze direction sensitivity)

Face recognition is present


Temporal lesions loss of object recognition and prosopagnosia

Temporal Lesions: Loss of Object Recognition and Prosopagnosia

Regions for face recognition have been demonstrated by fMRI studies include the FFA and PPA (temporal lobe) and overlap with object recognition regions Haxby et al, Science 293: 2425-2430 , 2001.

Neural basis of prosopagnosia… N. Hadjikhani and B. de Gelder, Human Brain Mapping, 16(3):176-182, 2002.


Visual attention solves the binding problem

Visual Attention: Solves the binding problem

  • The activity of V4 neurons is greatly enhanced by selective attention to the color of the matching stimulus (red)

  • Significance for the monkey is greatly increased for the matched (above) then the unmatched trials (below)


Attention causes activation of a parieto frontal pathway

Attention causes activation of a parieto-frontal pathway

  • Lack of attention to visual stimuli produced NO activation of the cortex (A)!

  • With attention to the peripheral target with discrimination, activation of a parieto-frontal pathway either directly (B) or in anticipation of target appearance (C).


An example of excellent depth and motion perception

An Example of Excellent Depth and Motion Perception


  • Login