NEUROSCIENCE Chapter 6 - Object Recognition

Computational Problems in Object Recognition

The challenges faced by the brain in accurately identifying objects despite variations in appearance due to changes in viewpoint, lighting conditions, and occlusion. These problems necessitate sophisticated visual processing mechanisms to maintain object constancy (Unified Perception and Precision)

Unified Perception

• Early visual areas use a “divide and conquer” strategy to separately IDENTIFY individual features of objects, such as color, shape, and motion.

• However, our PERCEPTION in UNIFIED. All of the information that is identified is brought together to form a coherent representation of the object. This processed can be lagged as information is being connected from many different sensory streams.

Unified Perception (Computational Problem in Object Recognition 1/2)

• Instead of using separate models for each task, this approach uses one model to do many things at once—like detecting objects, segmenting them, tracking them, and understanding the scene

• This increases processing and memory demands, creates conflicts between tasks, and makes the model more complex. Shared resources can also slow things down, especially in real-time systems.

Precision

The ability of the visual system to accurately identify and classify objects in varied and dynamic environments, ensuring that the recognition process remains consistent and reliable.

Precision (Computational Problem in Object Recognition 2/2)

• High precision can cause computational problems in object recognition because the model has to work harder to be very accurate.It often requires larger models, more detailed calculations, and more processing time. This increases memory use and slows down performance, especially in real-time systems.

• In short, aiming for very high precision can make the system less efficient and more resource-intensive.

Object Constancy

Objects can still be recognized as themself even when viewed at different angles, different depths, different illumination intensities, and even when they’re inverted or occluded (partially hidden).

Viewing Position

Visual perception relies heavily on the position and angle from which an object is seen, affecting its recognition and interpretation. Changes in depth and size are relative to our position.

Context

Our ability to recognize objects relies heavily on contextual information. This process is mediated by memory processes and our ability to categorize objects.

Multiple Pathways for Visual Perception (Visual Pathways)

Ungerleider and Mishkin (1982) Hypothesis

• The What (Ventral) Pathway (Object perception and recognition)

• The Where (Dorsal) Pathway (Spatial perception)

Ungerleider and Mishkin (1982) Hypothesis

This hypothesis posits that the brain has two distinct pathways for processing visual information: the ventral stream for object recognition and the dorsal stream for spatial awareness.

Ventral Stream (What?)

• Involved in the identification (the WHAT?) of objects

• Simple features processed in V1 are combined into more complex representations (receptive fields become larger and more complex)

• TEMPORAL lobe regions are connected with memory systems to aid in categorial identification

Involvement in Foveal Input

• Nearly 100% of the information contained in the VENTRAL system comes from foveal processing in V1

• We orient our foveal vision to objects that we are intending to identify

Dorsal Stream (Where?)

• Involved in determining the location (where?) of an object

• Relies on the PARIETAL Lobe

• This pathway determines the amount of spaces that an object takes up in the visual field

• Also involved in detecting the movement of objects through space

• This information is important for informing action areas of the premotor cortex

Audiotory Pathways

• These same computational goals are also evident in the auditory processing stream

• There are specific regions for determining what a sound is and others for determining where that sound came from

• There is a lot of overlap between visual and auditory processing streams

The Parahippocampal Place Area (PPA)

A region in the brain associated with the recognition of environmental scenes and spatial context. It plays a crucial role in processing and identifying places, showing heightened activity during visual scenes.

Evidence from Animal Models

• Cats were trained to do two different tasks: 1, Locate a sound, or 2, distinguish between two different types of sounds

• Tubes were inserted into the cat’s brains and delivered a cool liquid to temporarily activate either 1, the Anterior Temporal lobe or 2, the Posterior Temporal lobe

• Anterior temporal lobe inactivation made the cats unable to distinguish sounds, but they were still able to locate them

• Posterior Temporal lobe inactivation made the cats unable to locate sounds, but were still able to distinguish between sounds

Hierarchal (Sparse) Encoding

A method of coding visual information where only a small number of neurons respond to the presence of specific stimuli, enhancing efficiency and reducing redundancy in processing.

Ensamble Encoding

A method of coding where a group of neurons collectively responds to a stimulus, allowing for the representation of complex information through the combined activity of multiple neurons.

Grandmother/Jennifer Anniston Cells

Hypothetical neurons that activate specifically for individual objects or people, such as one's grandmother or Jennifer Aniston, suggesting a highly selective form of neural encoding in visual recognition systems.

From Primary to Association Areas

• As information travels from the primary visual cortex (V1) to unimodal association areas, receptive fields become more complex

• Simple lines at different orientations are put together into edges and corners

• Shapes are identified and combines to form objects

Object Recognition in Single Cells

• Gnostic Units

• Single cell recordings from cells in the anterior temporal cortex of monkeys showed complex receptive fields. Their cells would fire when shown a picture of a hand, wether it was a real hand, cartoon hand, human hand, or monkey hand

• This firing decreased significantly when the distinguishing features of the fingers were removed

Gnostic Units

Neurons that respond selectively to complex stimuli, such as specific objects or faces, contributing to the recognition of those stimuli in the brain.

The Halle Berry Experiment

• A study that identified neurons in the medial temporal lobe that respond specifically to images of Halle Berry, emphasizing the role of gnostic units in object recognition.

• Participants with intractable epilepsy were implanted with electrodes in the medial temporal lobe

• Certain cells responded selectively for particular actors or actresses (fired to Halle Berry, Halle Berry as Cat Woman, Halle Berry spelled or spoken out

• Disadvantages: Humans can recognize 10,000 - 30,000 objects, and experimenters used a very small range of stimuli and sampled a very small range of cells

Decoding

• A method used to predict what someone is doing just by using their brain activity

• Rather than looking at what brain region is most active for a task, researchers use the entire pattern activity for each stimulus, which are then used in subsequent trials to try and predict what the subject is doing or looking at

Evidence from MRI (Decoding)

• 2 subjects were shown 1750 images while being scanned, and patterns were collected in V1, V2, and V3. Subjects were then shown 120 new images and the computer reconstructed them images based on brain activity from the original images.

• Results showed that the brain activity patterns could accurately predict the images a subject was viewing, demonstrating the potential of decoding techniques in interpreting visual perception.

Decoding Dreams

A process of interpreting the neural activity associated with dreaming to understand the content and meaning of dreams. This involves analyzing patterns of brain activity while a subject is asleep, potentially providing insights into subconscious thoughts and experiences.

Face Perception

The process by which the human brain identifies, recognizes, and interprets faces, utilizing specific neural mechanisms and pathways to discern facial features, expressions, and identity.

Face Areas in Humans

• Specific regions in the brain, such as the fusiform gyrus (fusiform face area) and the superior temporal sulcus, that are specialized for processing faces. These areas play a critical role in face recognition and perception, responding more strongly to faces than to other objects. These regions are involved in detecting facial features and expressions, contributing to our ability to recognize and interpret faces across different contexts.

• Dozens of fMRI experiments have demonstrated that the fusiform face area is more receptive to face than other types of stimuli.

Fusiform Gyrus/ Fusiform Face Area (FFA)

• A region in the brain that is highly specialized for the perception and recognition of faces, known for its heightened activity in response to facial stimuli compared to other objects.

• Signals in the FFA are strongest when recognizing faces, but it also may be that this region computes information about things we find extremely important

Extrastriate Body Area

A region in the human brain that is specifically involved in the perception and recognition of human bodies and body parts. It is located along the lateral occipitotemporal cortex and plays a crucial role in processing body-related visual information.

Fusiform Body Area

A region in the brain involved in the perception and recognition of bodies and body parts, particularly responsive to body-related stimuli. It works in conjunction with the extrastriate body area to help decipher complex visual information about human figures.

Testing Causality

• MRI Research is Correlational

• In order to test causality, you need to be able to manipulate variables and observe changes

• This allows you to see that changes to the system are resulting in differences in behavioral outcomes

Perceptual Agnosia

A condition characterized by an inability to recognize objects, despite having intact sensory abilities. This typically results from damage to specific brain areas involved in object recognition.

Prosopagnosia

A neurological condition that impairs the ability to recognize faces, despite having normal vision and intelligence. It often results from damage to the fusiform gyrus, which is involved in facial recognition.

Autism

• A developmental disorder characterized by challenges with social interaction, communication, and restricted or repetitive behaviors. Symptoms can vary widely in severity and may affect daily functioning.

• Patients with autism also have difficulties related to face processing

• Less activity in FFA of Autistic patients than control subjects

Agnosia

• A disorder characterized by the inability to recognize and interpret sensory stimuli, despite having intact sensory pathways. This condition can manifest in various forms, such as object, visual, or auditory agnosia.

• Contains Apperceptive Agnosia and Associate Agnosia

Apperceptive Agnosia (Agnosia 1/2)

A type of agnosia where individuals have difficulty recognizing objects due to impairments in basic perceptual processes, despite having intact vision and simple feature processing. They may struggle to perceive the whole object even when its parts are identifiable.

Associative Agnosia (Agnosia 2/2)

A disorder where individuals can perceive objects but cannot associate them with their semantic meaning or name them, despite having intact visual pathways.

Holistic Analysis

A type of object recognition strategy in which individuals perceive the overall structure or configuration of an object rather than individual components. This approach helps in recognizing complex forms and patterns.

Analysis by Parts

A type of object recognition strategy where individuals break down objects into their constituent parts to recognize and identify them. This method contrasts with holistic analysis, focusing on details rather than overall configuration.

Acquired Alexia

A condition resulting from brain damage where an individual loses the ability to read despite having preserved language capabilities. It often involves difficulties in recognizing written words while maintaining intact writing and speaking abilities.

Apperceptive Ataxia

A neurological disorder characterized by an inability to recognize objects due to impaired visual integration, often resulting from brain damage. Individuals may have difficulty understanding the visual properties of objects, despite having intact sensory function.

Acquired Agraphia

A writing disorder resulting from brain damage, where individuals lose the ability to write while retaining other language skills. It often involves difficulties in forming letters or words, despite understanding language.