multiplechoicequestions.docx

Object Recognition ------------------ 6 = \ OUTLINE **219** ### Principles of Object Recognition Principles of Object Recognition \| **221** Fourth, *tλe pvoduct of pevception ė also intimately in-* *tevwoven witλ memovy.* Object recognition is more than TAKE-HOME MESSAGES - Sensation, pe...

Object Recognition ------------------ 6 = \ OUTLINE **219** ### Principles of Object Recognition Principles of Object Recognition \| **221** Fourth, *tλe pvoduct of pevception ė also intimately in-* *tevwoven witλ memovy.* Object recognition is more than TAKE-HOME MESSAGES - Sensation, perception, and recognition refer to distinct phenomena. - People perceive an object as a unified whole, not as an entity separated by its color, shape, and details. - Although our visual perspective changes, our ability to recognize objects remains robust. - Memory and perception are tightly linked. - Patients with visual agnosia are unable to recognize common objects presented to them visually. This deficit is modality specific. Patients can recognize an object when they touch, smell, taste, or hear it. ### Multiple Pathways for Visual Perception a. The longitudinal fasciculus, shown here in shades of purple. b. The ventral "what" pathway terminates in the inferotemporal cortex, and the dorsal "where" pathway terminates in the posteroparietal cortex. The initial data for the what--where dissociation of the ##### Representational Differences Between the Dorsal and Ventral Streams 1 2 3 4 5 6 ##### Perception for Identification Versus Perception for Action Lateral TAKE-HOME MESSAGES - The ventral stream, or occipitotemporal pathway, is specialized for object perception and recognition. This is often referred to as the "what" pathway. It focuses on "vision for recognition." - The dorsal stream, or occipitoparietal pathway, is specialized for spatial perception and is often referred to as the "where" or "how" pathway. It focuses on "vision for action." - Neurons in the parietal lobe have large, nonselective receptive fields that include cells representing both the fovea and the periphery. Neurons in the temporal lobe have large receptive fields that are much more selective and always represent foveal information. - Patients with selective lesions of the ventral pathway may have severe problems in consciously identifying objects, yet they can use the visual information to guide coordinated movement. Thus we see that visual informa- tion is used for a variety of purposes. - Patients with optic ataxia can recognize objects but cannot use visual information to guide action. Optic ataxia is associated with lesions of the parietal cortex. ### Computational Problems in Object Recognition Dorsal view ##### Variability in Sensory Information ##### View-Dependent Versus View-Invariant Recognition ##### Shape Encoding 0 New New Familiar Novel Scrambled a. Stimuli for the three conditions and the mental operations required in each condition. Novel objects are hypothesized to engage processes involved in perception even when verbal labels do not exist. b. Activation was greater for the familiar and novel objects compared to the scrambled images along the ventral surface of the occipitotemporal cortex. ##### Grandmother Cells and Ensemble Coding OFL 1. The idea of grandmother cells rests on the assumption that the final percept of an object is coded by a single cell. Because cells are constantly firing and re£actory, a coding scheme of this nature would be highly susceptible to error. If a gnostic unit were to die, we would expect to experience a sudden loss for an object. You would pass grandma (or Halle Berry) on the street without a second thought. 2. The grandmother-cell hypothesis cannot adequately account for how it is possible to perceive novel objects. 3. Third, the gnostic theory does not account for how the grandmother cell would have to adapt as ##### Summary of Computational Problems - The lateral occipital cortex is critical for the recognition of the shape of an object. - The term *grandmother cell* has been coined to convey the notion that recognition arises from the activation of neurons that are finely tuned to specific stimuli. - Ensemble theories, on the other hand, hypothesize that recognition is the result of the collective activation of many neurons. ### Failures in Object Recognition: The Big Picture the effects of the disease or injury on attention, memory, and language. Unlike someone with visual agnosia, for a TAKE-HOME MESSAGES - Object constancy refers to the ability to recognize objects in countless situations, despite variation in the physical stimulus. - Object perception may occur in a view-dependent frame of reference or a view-invariant frame of reference. In view-dependent theories, perception is assumed to be specific to a particular viewpoint. View-invariant theories posit that recognition occurs at a level that is not linked to specific stimulus information. TAKE-HOME MESSAGES - Category-specific deficits are deficits of object recognition that are restricted to certain classes of objects. - Prosopagnosia is an inability to recognize faces that cannot be attributed to deterioration in intellectual function. - Acquired alexia is characterized by reading problems that occur after a patient has a stroke or head trauma. - Neurons in various areas of the monkey brain show selectivity for face stimuli. - Similarly, specificity is observed in fMRI studies, includ- ing an area in the fusiform gyrus of the temporal lobe, the fusiform face area, or FFA. - Analytic processing is a form of perceptual analysis that emphasizes the component parts of an object, a mode of processing that is important for reading. - Holistic processing is a form of perceptual analysis that emphasizes the overall shape of an object, a mode of processing that is important for face perception. - Just as the FFA is specialized for processing faces, the parahippocampal place area (PPA) is specialized for processing information about spatial relations or for classifying objects based on spatial properties (e.g., an indoor vs. outdoor scene). - Likewise, the extrastriate body area (EBA) and the fusi- form body area (FBA) have been identified as more active when body parts are viewed. ### Mind Reading ##### Encoding and Decoding Brain Signals BOLD Response Stimulus ##### Statistical Pattern Recognition \+ 0 -- Orientation (˚) a. Receptive field encoding b. Mind reading by decoding fMRI activity to visual images. 1. Measure brain activity for an image. 2. Predict brain activity for a set of images using receptive field models. 3. Select the image ( ) whose predicted brain activity is most similar to the measured brain activity. 120 90 60 30 --1 --0.5 0 0.5 1 ##### A Look Into the Future of Mind Reading 30 60  \ TAKE-HOME MESSAGES - Encoding models are used to predict the physiological response, such as the BOLD response to a stimulus. - Decoding models are used in the reverse manner, predicting the stimulus (or mental state) based on a physiological response such as the BOLD activity across a set of voxels. Mind reading may one day be used to communicate with people who are currently unable to speak