Dorsal vs. Ventral Pathway Overview

• Dorsal Pathway (Where Pathway)

  • Concerned with object recognition and spatial representation.

  • Receives information about:

  • Color

  • Orientation

  • Form

  • Key functions include:

  • Representing locations of objects

  • Tracking speed and direction of motion

  • Manipulating objects

  • Damage can lead to spatial neglect, where individuals may neglect one side of space.

• Ventral Pathway (What Pathway)

  • Primarily dedicated to processing visual information related to object recognition.

  • Encompasses areas of the occipitotemporal and temporal regions.

  • Posterior regions respond to simple stimuli.

  • Cells further along the stream react to complex and specific stimuli.

  • Larger receptive fields develop as one moves along the pathway, allowing object identification regardless of size or spatial location, albeit some positional information is lost.

Visual Processing Streams

The Ventral Visual Processing Stream

• Composed of regions in occipitotemporal and temporal areas responsible for object recognition.

  • Posterior regions: respond to simple stimuli.

  • Further along: respond to complex stimuli.

• Receptive Fields

  • Receptive fields increase in size as one progresses through the ventral stream, resulting in loss of specific positional information.

Agnosia Types

General Characteristics of Visual Agnosia

• Inability to recognize objects visually not explained by other causes,

• Modality Specific: Primarily manifests in the visual sense.

• Two major types:

  • Apperceptive Visual Agnosia:

  • Fundamental difficulty in forming a perceptual whole from sensory input.

  • Despite basic processing of sensory information, the connections to meaningful objects are lost.

  • Associated with right hemisphere damage.

  • Difficulty observing objects in degraded states and at nonstandard orientations.

  • Associative Visual Agnosia:

  • Ability to assemble complex stimuli but inability to connect them to stored knowledge.

  • Patients can draw objects but struggle to name them.

  • Typically linked to left hemisphere damage.

Distinguishing Apperceptive from Associative Agnosia

• Apperceptive Visual Agnosia

  • Diffuse damage typically at the occipital lobe.

• Associative Visual Agnosia

  • Damage in occipitotemporal regions.

Category-Specific Agnosia

• Certain patients face difficulty naming living things over nonliving objects, while others may experience the opposite.

• Prosopagnosia:

  • Selective inability to recognize faces, tied to right ventral stream damage.

  • Individuals retain basic ability to perceive faces but cannot recognize them as belonging to specific individuals.

  • Developmental prosopagnosia affects approximately 2% of the population.

• Fusiform Face Area (FFA):

  • Located in the fusiform gyrus, most active during face recognition.

  • Left hemisphere active in word recognition.

  • Some activity on the right for discrimination tasks involving specific categories (e.g., birds, cars).

Recognition and Processing of Faces

Prosopagnosia Insights

• Mixed results on whether only faces are uniquely affected in prosopagnosia.

• Some patients show difficulties with other complex discriminations beyond faces.

• Examples illustrating this:

  • A farmer failed to recognize his cows post-prosopagnosia.

  • A birdwatcher could not distinguish between bird species.

• Additional case studies:

  • Patient W.J.: Learned to recognize sheep but could not identify humans.

  • Patient L.H.: Could distinguish eyeglasses normally but was impaired in face recognition.

The Thatcher Illusion

• A perceptual phenomenon demonstrating poorer recognition when an object is inverted.

• Highlights importance of configural information in recognizing items of expertise.

Object Recognition Mechanisms

Viewpoint-Dependency in Recognition

• Recognition influenced by current viewpoint, suggesting reliance between stored descriptions and sensory input.

• Research indicates:

  • Left ventral stream: focuses on object parts.

  • Right ventral stream: focuses on holistic forms.

Conjunctive vs. Nonlocal Binding Encoding

• Conjunctive Encoding:

  • Proposes hierarchical feature linking through features processing.

• Nonlocal Binding:

  • Whole objects represented by simultaneous activation without distinct representations.

Category-Specific Activation Areas

• Face recognition is crucial, with evidence indicating specific treatment of faces in the human brain.

• Evidence from primate studies shows specialized neurons respond directly to face components.

• Fusiform Face Area:

  • Critical for face recognition with distinct neural activity.

• Theoretical acknowledgment of a face-specific module remains debated.

Object Recognition in Other Modalities

Tactile and Auditory Object Recognition

• Humans recognize objects through various modalities beyond vision:

  • Auditory agnosia (

  • Definition: inability to recognize meaningful sounds, manifesting in verbal, nonverbal, and mixed forms.

  • Tactile agnosia (somatosensory agnosia): inability to recognize objects by touch.

  • Tactile object recognition involves the LOC, linking touch and visual recognition but operating autonomously.

  • Auditory object recognition parallels visual recognition with areas being activated for familiar voices.

Conclusion: What vs. Where Pathways Across Modalities

• The distinction between “what” (object recognition) and “where” (location recognition) pathways transcends specific modalities across sensory systems, with ventral stream for the “what” and dorsal for the “where.”