Perception - Visual Perception in Psychology, Lecture Slides PDF

Perception Agenda Perception and Factors Affecting Perception Visual Perception ○ From Eye to Brain The retina Primary visual cortex (V1) Visual processing pathways beyond V1 ○ Object recognition Speech Perception Multimodal perception Perception Th...

Perception Agenda Perception and Factors Affecting Perception Visual Perception ○ From Eye to Brain The retina Primary visual cortex (V1) Visual processing pathways beyond V1 ○ Object recognition Speech Perception Multimodal perception Perception The brain is involved in actively constructing a visual representation of the world ○ Not a literal reproduction of the pattern of light falling on the eyes The brain is biased to perceive objects when there is not necessarily an object there The brain makes inferences during visual perception that go beyond the raw information given Kanizsa illusion Perception Our sensory receptors collect information about our environment, but it is then how we interpret that information that ultimately affects how we interact with the world Perception – way that sensory information is interpreted, organized, and consciously experienced Perception involves two forms of processing: ○ Bottom-up processing – system in which perceptions are built from sensory input ○ Top-down processing – interpretation of sensations is influenced by available knowledge, experiences, and thoughts Factors Affecting Perception Sensory adaptation–not perceiving stimuli that remain relatively constant over prolonged periods of time Motivation Beliefs, values, prejudices and expectations … Factors Affecting Perception Attention ○ Process of concentrating on specific features in the environment, thoughts, or activities ○ Often to the exclusion of other information Inattentional blindness: Failure to notice something that is completely visible because of a lack of attention Factors Affecting Perception Inattentional blindness https://www.youtube.com/watch?v=vJG698U2Mvo&list=PLB228A1652CD49370 Factors Affecting Perception Change blindness https://www.youtube.com/watch?v=FWSxSQsspiQ&list=PLC0A3CAC7B3A0E288 Factors Affecting Perception Language The Sapir-Whorf Hypothesis: The structure of a language influences the way its speakers perceive and think about the world Color perception ○ The Himba Tribe Study From Eye to Brain Visual perception involves the processing of information conveyed by light energy that enters the eye The Retina The internal surface of the eyes that contains specialized photoreceptors that convert (or transduce) light into neural signals Rods: Specialized for low levels of light intensity Cones: Specialized for high levels of light intensity, and for the detection of different wavelengths Cones are packed more densely in the center of the retina (the fovea), rods are located more in the periphery The Retina Relayed to the brain via optic nerves Blind spot: The point at which the optic nerve leaves the eye ○ No rods and cones present here From Eye to Brain Light energy: a. enters the eye through the cornea b. passes through a small opening called the pupil (pupil size is controlled by the iris) c. is refracted through the lens d. is then focused on the tissue at the back of the eye known as the retina e. where it is captured by light receptors called photoreceptors (most densely packed in the fovea) and changed it into a neural signal The neural signal is then transmitted to the brain through the optic nerve Primary Visual Cortex (V1) The optic nerve of each eye merges at the optic chiasm, an X-shaped structure just below the cerebral cortex The dominant visual pathway in the human brain travels to the primary visual cortex (V1 or striate cortex) via a processing station called the lateral geniculate nucleus (LGN) Primary Visual Cortex (V1) Primary visual cortex is the area at the back of the brain responsible for the early processing of the visual signal and involved in visual consciousness ○ How light or dark something is ○ The color of an object ○ Edges (abrupt changes in brightness or color) ○ Movement ○ Depth ○ … Primary Visual Cortex (V1) There are several types of primary visual cortex cells (pioneering work by David Hubel and Torsten Wiesel) ○ E.g., cells that respond to light in particular orientations, particular lengths https://www.youtube.com/watch?v=y_l4kQ5wjiw Primary Visual Cortex (V1) The primary visual cortex is retinotopic: the mapping of visual input from the retina to neurons https://www.youtube.com/watch?v=HCLgh9AwvrQ Beyond V1 There are two distinct visual processing pathways Visual Processing Pathways Connections between visual areas are bi-directional Feedforward (“bottom-up”): visual information from the primary visual cortex → the “what” and “where” pathways Feedback (“top-down”): Regions at the ends of the ventral and dorsal pathways → the primary visual cortex Top-down Processing in Visual Perception Try reading the following sentence: For epxeirecned redares, ltetres dno’t hvae to be in the rhigt palecs. Jumbled word effect: the ability to raed wdors in steentnecs evne wneh smoe of the lttrees rea meixd up Top-down Processing in Visual Perception Word superiority effect: It’s easier to identify a letter (e.g., p) if it appears in a word (e.g., warp) than if it appears alone or in a non-word (e.g., awrp) Reicher's Experiment (1969): ○ Objective: To investigate the influence of contextual information on letter recognition ○ Method: Participants were presented with a letter string briefly and asked to identify a specific letter within the string ○ Conditions: The letter strings were either real words or non-word letter strings ○ Results: Participants were faster and more accurate at identifying the target letter when it was embedded in a real word compared to a non-word string ○ Conclusion: The contextual information provided by real words facilitated letter recognition, showcasing the role of top-down processing in visual perception Visual Processing Pathways Visual processing is highly modular ○ “Divide and conquer” Some visual deficits caused by damage to specific areas of the brain Visual Processing Pathways V4: A region of the extrastriate cortex associated with color perception Achromatopsia: A failure to perceive color (the world appears in grayscale) ○ Rare Visual Processing Pathways V5 (or MT): A region of the extrastriate cortex associated with motion perception Akinetopsia: A failure to perceive visual motion https://www.youtube.com/watch?v=BIalOjDwZzU “What” vs. “Where”/”How” “What” vs. “Where”/”How” Goodale et al. (1991) reported on patient DF with visual agnosia ○ DF was unable to identify objects visually as a result of damage to the ventral stream ○ DF was still able to act on objects: intact dorsal stream Jakobson et al. (1991) reported on patient VK with optic ataxia ○ VK was unable to properly change grip aperture when attempting to grasp objects due to damage to the dorsal visual pathway ○ VK was still able to visually identify objects: intact ventral stream “What” vs. “Where”/”How” Optic ataxia = spared “what”, impaired “where”/“how” Poor visual guidance of reaching (parietal lobe damage, dorsal stream) “What” vs. “Where”/”How” Optic ataxia https://www.youtube.com/watch?v=BkOb9FR5Lgk Visual Processing Pathways Different types of visual information get parsed into more specialized brain regions The question of how these different streams of information come back together (if at all) is not well understood, but may require the involvement of non-visual processes related to attention Object Recognition Initial Stage: Detection of basic visual elements like edges and bars Intermediate Stage: Grouping basic elements into higher-order units that code depth cues and segregate surfaces into figure and ground Advanced/Final Stage: Recognizing the object and attributing meaning to it Feature Detection Detecting patterns on the basis of their features or properties Selfridge’s (1959) pandemonium model is a model of pattern recognition consisting of three levels: ○ Features: the bottom-level model consists of properties of the stimulus such as size, color, shape, etc. ○ Cognitive demons: the next level decides whether the stimulus matches its particular pattern ○ Decision demon: the top level decides which pattern is being recognized based on the input of the cognitive demons Feature Detection Easy to compile a list of basic features for letters or words Get complicated for three-dimensional objects Recognition by Components Decomposing objects into fundamental 3D geometric shapes (geons) and comparing with existing memory representations Recognition by Components Accounts for how we are able to recognize objects from different viewpoints Recognition by Components Makes verifiable predictions about which viewpoints should be more difficult to recognize objects Gestalt Grouping Principles Perception is holistic in nature rather than atomistic and that the grouping of visual features to form a whole follows certain organizational principles (a) law of proximity (b) law of similarity (c) law of good continuation (d) law of closure Template Matching Comparing the configuration of the current sensory input with a standard configuration we have in memory (a prototype or template) Visual Agnosia Apperceptive agnosia: A failure to understand the meaning of objects due to a deficit at the level of object perception Associative agnosia: A failure to understand the meaning of objects due to a deficit at the level of semantic memory This classification may be too simple ○ Can be broken down into even finer processes ○ Interactivity between different processes Visual Agnosia Case HJA: seeing the parts but not the whole ○ Integrative agnosia: A failure to integrate parts into wholes in visual perception Visual Agnosia https://www.youtube.com/watch?v=ze8VVtBgK7A Face Recognition Face recognition is a within-category discrimination (all faces look the same), whereas other object recognition is between category (e.g. distinguishing a pen from a cup) Maybe faces require different types of processing to other objects? Maybe faces are so important from a social/evolutionary perspective that they have a mechanism all to themselves? = domain-specificity Face Recognition Cognitive model: Bruce and Young (1986) ○ Face recognition units (FRUs): Stored knowledge of the three-dimensional structure of familiar faces ○ Person identity nodes (PINs): An abstract description of people that links together perceptual knowledge (e.g., faces) with semantic knowledge Face Recognition Fusiform face area (FFA): An area in the inferior temporal lobes that responds more to faces than other visual objects, and is implicated in processing facial identity Face Recognition Prosopagnosia: Impairments of face processing that do not reflect difficulties in early visual analysis ○ Also used specifically to refer to difficulty in recognizing previously familiar faces De Renzi (1986) – patient failed to recognize his own family but could do so by voice, clothes “are you…? [wife’s name] I guess you are my wife because there are no other women at home, but I want to be reassured” Could match different views of faces and name other objects Face Recognition Prosopagnosia https://www.youtube.com/watch?v=vwCrxomPbtY Speech Perception Auditory Perception Sound is composed of waves ○ The frequency of the wave is perceived as pitch ○ The amplitude of the wave is perceived as loudness Auditory Perception https://www.youtube.com/watch?v=yMLTF_0PAQw Speech Stream In a written text, each letter is a discrete symbol, and each word is separated from its neighbors by spaces. The speech stream doesn’t consist of discrete phonemes and clear word boundaries. ○ A continuous flow of ever-changing frequencies and amplitudes Speech sounds smear into each other ○ Coarticulation: process of overlapping phonemes in the speech stream ○ Results from the fact that it takes time for the tongue, jaws, and lips to move from one position to another E.g., can or ham ○ Coarticulation also increases the transmission rate of the speech signal We can say more in less time by overlapping speech sounds Variability ○ Between speakers ○ Within speakers over time Speech Perception Lack of invariance ○ No reliable relationship between a phoneme and the acoustic signal Speech perception: to infer intended phonemes and word boundaries on the basis of multiple cues within the speech stream Speech perception requires the auditory system to: ○ record sound vibrations of someone talking ○ translate vibrations into a sequence of sounds that you perceive to be speech ○ distinguish the sound pattern of one word from all other irrelevant words ○ separate voice of speaker from background noise, including other conversations Speech Perception Context and speech perception (top-down processing) Phonemic restoration: The process of filling in missing segments of the speech stream with contextually appropriate material E.g., Warren and Warren (1970) ○ It was found that the *eel was on the axle. When the gap was filled with a cough, participants said they heard the missing wh ○ It was found that the *eel was on the shoe. Participants reported hearing the word heel when the gap was filled with a cough Speech Perception Phonemic restoration https://www.youtube.com/watch?v=ZyvyGMkzNQc Multimodal Perception The modality appropriateness hypothesis posits that different senses are better at processing different stimuli, therefore depending on the circumstances, different sensory modalities will dominate at different times Visual prepotency effect is the hypothesis that the visual system dominates the other senses when it comes to perceptual processing ○ Conflict Resolution: In situations where visual and auditory information conflict, individuals often rely more on visual information to resolve the conflict Vision and Audition https://www.youtube.com/watch?v=aFPtc8BVdJk Vision and Audition McGurk Effect ○ Audio record a person producing the sound /ba/ and video record the same person producing the sound /ga/ ○ If you only listen to the audio recording, you will perceive /ba/ ○ If you only watch the video recording, you will perceive /ga/ ○ If you listen to the audio and watch the video at the same time, you will perceive /da/ /da/ is a speech sound halfway between /ba/ and /ga/ Vision and Audition https://www.youtube.com/watch?v=G-lN8vWm3m0