feb 3 flashcards

Understanding Visual Processing

• Feature Detectors

  • Neurons in the visual cortex are specifically tuned to respond to particular features in the visual field such as lines and orientations.

  • Example: Neurons that respond to vertical lines will fire intensely when a vertical line stimulus is presented.

• Adaptation to Stimuli

  • When exposed to a stimulus for a prolonged period, specific feature detectors adapt, resulting in decreased firing rates.

  • This phenomenon is known as selective adaptation and shows how neurons become fatigued in their response to the prolonged stimulus.

• Example of Selective Adaptation

  • Observers may see a morph image differently depending on which individual’s face they focused on first (e.g., DiCaprio vs. Freeman).

  • Initial neurons responding to the focused face become fatigued, while those for the non-focused face remain active, leading to biased perception.

Sensory Adaptation in Daily Life

• Adaptation can occur across all senses:

  • Temperature: Jumping into a cold pool feels shocking at first but becomes less intense as your body adapts.

  • Touch: New clothing initially feels very present but becomes less noticeable over time as receptors adapt.

Experience-Dependent Plasticity

• Extended exposure to specific stimuli can lead to structural changes in the brain, which is termed experience-dependent plasticity.

• Research with Kittens

  • Kittens raised in environments dominated by vertical lines develop a visual cortex with no neurons responding to horizontal lines due to lack of exposure.

  • This showcases that early visual experiences significantly shape neural development and capabilities.

Visualization and Retinotopic Organization

• Cortical Magnification

  • The visual cortex dedicates about 10% of its area to processing the fovea—a tiny spot on the retina that collects detailed visual information.

• Retinotopic Mapping

  • There is a spatial organization in the visual cortex that mirrors the layout of the retina, where adjacent areas in the visual field correspond to adjacent neurons in the cortex.

• Neuron Organization

  • Research has identified location columns in the cortex, which respond to specific locations in the visual field, and they contain orientation columns responsible for detecting line orientations.

The Dorsal and Ventral Streams

• The visual pathways process different aspects of visual information:

• Dorsal Stream

  • Involved in spatial awareness (where an object is).

  • Impaired in patients with damage to this pathway affects the ability to locate objects (landmark discrimination task).

• Ventral Stream

  • Responsible for object identification (what an object is).

  • Damage here affects the ability to recognize objects despite spatial awareness being intact (object discrimination task).

Double Dissociation and Independent Pathways

• Case Study of Patient DF

  • Despite damage to the ventral stream leading to poor performance in perceptual tasks, DF performed well in action tasks, demonstrating that the two streams function independently.

• Dissociation in Visual Processing

  • Comparisons of performances in tasks help establish that these pathways are not just variations of difficulty but represent distinct functional systems.

The Inferotemporal Cortex

• Complex Object Recognition

  • The inferotemporal cortex is crucial for recognizing complex shapes and objects, including hands and faces.

  • Neurons in this area respond to specific shapes rather than just simple lines, showcasing higher-level visual processing.

Understanding Visual Processing

Feature Detectors

Neurons in the visual cortex are specifically tuned to respond to particular features in the visual field, such as lines, orientations, colors, and motion. These specialized cells allow for the analysis of visual stimuli with great efficiency and accuracy. For example, neurons that respond to vertical lines will fire intensely when a vertical line stimulus is presented, while other neurons may respond to horizontal lines or diagonal orientations. This selective sensitivity is crucial for facilitating human perception of complex visual environments.

Adaptation to Stimuli

When individuals are exposed to a stimulus for a prolonged period, certain feature detectors undergo adaptation, leading to decreased firing rates over time. This phenomenon, known as selective adaptation, demonstrates how neurons can become fatigued or less responsive in their reactions to a continuous stimulus. A pertinent example of selective adaptation occurs when observers see a morph image differently depending on which individual’s face they have focused on first (e.g., DiCaprio vs. Freeman). The neurons initially responding to the focused face become fatigued, while those encoding the non-focused face remain active, ultimately influencing biased perceptions.

Sensory Adaptation in Daily Life

Adaptation can occur across all senses and serves as an essential mechanism through which we tune into our environments.

• Temperature Sensation: For instance, jumping into a cold pool induces an intense cold shock sensation initially; however, this sensation diminishes as the body adapts to the water temperature.

• Touch Sensation: Similarly, wearing new clothing initially feels very present due to tactile receptors firing intensely, but this feeling often fades and becomes less noticeable over time as the receptors adapt.

Experience-Dependent Plasticity

Extended exposure to particular stimuli can lead to structural changes in the brain, a concept known as experience-dependent plasticity.

• Research with Kittens: A compelling illustration of this is found in studies with kittens raised in environments dominated by vertical lines. Their visual cortex develops with a lack of neurons responding to horizontal lines due to insufficient exposure. This underscores the importance of early visual experiences in shaping neural development and cognitive capabilities.

Visualization and Retinotopic Organization

Cortical Magnification

The visual cortex dedicates about 10% of its total area to processing the fovea, a tiny yet highly sensitive spot on the retina responsible for detailed visual information collection and analysis. This extensive dedication indicates the priority given to high-resolution visual processing for tasks such as reading and recognizing faces.

Retinotopic Mapping

Within the visual cortex, there exists a spatial organization that mirrors the layout of the retina. Adjacent areas in the visual field are represented by adjacent neurons in the cortex, creating a retinotopic map essential for visual localization.

Neuron Organization

Research has identified location columns within the cortex that respond to specific locations in the visual field. These columns contain orientation columns that are responsible for detecting specific line orientations at those locations—further enhancing the visual system's ability to detect and comprehend complex scenes.

The Dorsal and Ventral Streams

The visual pathways are divided into two streams that process different aspects of visual information.

• Dorsal Stream: Responsible for spatial awareness, the dorsal stream helps in determining where an object is located in space. Patients with damage to this pathway exhibit difficulties in locating objects and typically perform poorly in landmark discrimination tasks.

• Ventral Stream: This stream is associated with object identification—essentially answering the question of what an object is. Damage to the ventral stream can impair the ability to recognize objects, even when spatial awareness remains intact. This is often illustrated in object discrimination tasks where affected individuals struggle to identify familiar items, despite being able to accurately describe their positions in space.

Double Dissociation and Independent Pathways

Case Study of Patient DF

A notable exploration of this concept is illustrated in the case study of Patient DF, who suffered damage to the ventral stream. Despite her poor performance in perceptual tasks related to object identity, DF performed exceptionally well in action tasks, such as reaching for objects, indicating that these two pathways function independently and support different aspects of visual processing.

Dissociation in Visual Processing

Comparative analyses of performances across tasks have demonstrated that the dorsal and ventral streams are not merely variations of difficulty; rather, they represent distinct functional systems within the visual processing architecture of the brain.

The Inferotemporal Cortex

Complex Object Recognition

The inferotemporal cortex plays a critical role in recognizing complex shapes and objects, including human hands and faces. Neurons located in this area respond to specific and intricate shapes as opposed to simple lines, thus showcasing higher-level visual processing capabilities that are fundamental for tasks like facial recognition and the categorization of various objects in our environment.