Lecture 2 Sensation/Perception PDF

Lecture Monday, January 6, 2025 1:25 PM Sensation/Perception Part 1: The Five Senses: - Vision - Hearing - Touch - Taste - Smell - Without these 5 senses, our brains would not be able to process anything about our world. Sensation vs. Percepti...

Lecture Monday, January 6, 2025 1:25 PM Sensation/Perception Part 1: The Five Senses: - Vision - Hearing - Touch - Taste - Smell - Without these 5 senses, our brains would not be able to process anything about our world. Sensation vs. Perception: - Sensation: the process through which the senses pick up visual, auditory, and other sensory stimuli and transmit them to the brain; sensory information that has registered in the brain but has not been interpreted. - Perception: the process by which sensory information is actively organized and interpreted by the brain. What is it like to be a Bat? - Bats use echolocation, for most humans, this is something we never experience. ○ Echolocation: the location of objects by reflected sound, in particular that used by animals - Most animals possess some sensory ability that is absent in humans ○ Birds are thought to use earth’s magnetic field to migrate ○ Mantis shrimp detect polarized light Why is Understanding Sensory Systems Important? - All cognitive processes are influenced, at least initially, by sensory input. ○ This makes the understanding of sensory system evolution, development, and function across species very important. - Sensory systems provide the first point of contact between an organism and its environment. - Need to understand: 1. Evolution 2. Development 3. Function n  - Sensory systems provide the first point of contact between an organism and its environment. - Need to understand: 1. Evolution 2. Development 3. Function 1 - Evolution of Sensory Systems: - Humans see vibrant colour in flowers, but not UV reflections which guide insects. - Humans detect odor, but could not track another human or animal like a dog. - Human auditory systems is finely tuned to range of sound frequencies in speech, an advantage for verbal communication. - Visual information is also extremely important for humans, so we have evolved a comple visual system. Visual Adaptation: - In all animals, the visual system works by absorbing light of particular wavelengths along the electromagnetic spectrum. - Humans see within 400-700nm range, because we have pigments in the eye to absorb these wavelengths. - Different animals in different habitats have evolved different visual sensitivities. - Evolution has also favoured traits that help animals see based on different lifestyles. - Compared to diurnal animals, nocturnal animals have larger lenses that pick up more ligh - The tapetum lucidum (located behind the retina) also aides in the night vision of many animals, particularly nocturnal animals. Eye Placement: - Binocular vision occurs when the two visual fields overlap. - The brain uses the disparity between the right and left eye to create depth perception, or  lifestyles. - Compared to diurnal animals, nocturnal animals have larger lenses that pick up more light. - The tapetum lucidum (located behind the retina) also aides in the night vision of many animals, particularly nocturnal animals. Eye Placement: - Binocular vision occurs when the two visual fields overlap. - The brain uses the disparity between the right and left eye to create depth perception, or stereopsis. - Prey animals tend to have laterally placed eyes, resulting in less depth perception, but an extremely large field of view. - Predators tend to have more forward-facing eyes, resulting in excellent depth perception, but very poor lateral vision. Timney & Keil (1999) - Stereopsis in Horses - Horses have laterally placed eyes...do they have enough binocular overlap to detect depth perception? - Horses successfully trained to discriminate flat (+) stimulus from protruding (-) stimulus. Rods, Cones, and Retinal Ganglion Cells: - Rods and cones are photoreceptors at the back of the eye that detect light and colour. ○ Rods = Better Night Vision ○ Cones = Better Colour vision - Nocturnal animals tend to have far more rods than diurnal animals. ○ Rods are 1000x more sensitive to light than cones ○ Nocturnal animals navigate very well in the dark but often have inferior colour vision. - Retinal Ganglion cells are neurons that are the “last stop” in the eye ○ Information from the photoreceptors in the retina is passed to the optic nerve and sent to the brain. Human Vision vs. Dog Vision: (Treat the below numbers as approximations, as slightly different numbers have been reported) - Humans (diurnal): ○ 0.7-1.5 million retinal ganglion cells ○ 4.6 million cones ○ 92 million rods ○ Trichromat colour vision ○ Have densely packed cones in the fovea, which is responsible for sharp  - Humans (diurnal): ○ 0.7-1.5 million retinal ganglion cells ○ 4.6 million cones ○ 92 million rods ○ Trichromat colour vision ○ Have densely packed cones in the fovea, which is responsible for sharp central vision. - Dogs (arrhythmic diurnal...NOT nocturnal): ○ 115, 000 retinal ganglion cells (Peichl, 1992) ○ Far more rods than cones ○ Dichromat colour vision ○ Retinal Ganglion Cells arranged in “visual streak” Sensory Adaptation in Closely Related Species: - Snakes can detect chemical, visual, and thermal cues, but they may show greater sensitivity depending on their preferred prey. - The Midland rat snake feeds on rodents, and responds to chemical cues allowing them to follow odour trails. - Western fox snakes respond more to visual cues in order to hunt ground nesting birds. Sensory Drive Hypothesis: - Explains divergence of sensory abilities both between and within species. ○ Facilitates communication - Developing different sensory abilities either between or within species is costly, so these capacities are lost or not developed unless needed - Animals become separated by a geographical barrier (ex: mountain range). - New habitat has features that make it easier or harder to communicate in the old territory. - Ex: If birds move into a territory with denser trees, lower light would make it difficult for females to detect bright plumage on males. - Therefore, females with better visual acuity and males with brighter feathers, have new advantage that was not present in old habitat. Sensory Bias: - A paradox of the evolution of sensory systems. - Occurs in situations in which individuals of a species respond with increased vigour to stimuli that are exaggerated versions of naturally occurring stimuli. - Ex: Experiments using artificial tails in Paradise Whydah Sensory Exploitation: - When sensory signals which were important for one process have been co- opted by another. - Female Zebra finches need white feathers to build nests. Their interest in the  - Ex: Experiments using artificial tails in Paradise Whydah Sensory Exploitation: - When sensory signals which were important for one process have been co- opted by another. - Female Zebra finches need white feathers to build nests. Their interest in the adorned males has nothing to do with male fitness, but rather is a “borrowed” response from their nest building behaviour. Supernormal Stimuli: - The principles of sensory exploitation may also explain heightened responses to exaggerated versions of natural stimuli. - Tinbergen (1951): graylag geese retrieve and attempt to incubate giant artificial eggs - Even when their actual eggs sat nearby. - Stickleback fish will ignore invading conspecifics in favour of attacking wooden dummy fish with darker red undersides. In Summary: - An enormous range of sensory abilities exists across the animal kingdom. - All animals experience only a portion of the sensory world, and these generally reflect the evolutionary history of that species. 2 - Development of Sensory Systems: - Much of what is known regarding sensory system development comes from pioneering work by Hubel & Wiesel (who won the 1981 Nobel prize for their description of how the visual system is processed and organized in the brain). - Found that when young monkey or kittens are deprived of vision for as little as 1 week, normal vision never develops. - BUT...visual deprivation for weeks or even months in adults has no effects on vision. - Cells in the eye respond normally after deprivation, however neurons in the cortex that receive signals from these cells do not. - Sensitive Period: The period in which experience-dependent changes can have profound and enduring effects on development. Blakemore (1976) - If cats are exposed to a particular visual stimulus during the first few weeks of life (horizontal versus vertical lines), their ability to detect the previously exposed pattern is enhanced in adulthood. - This shift in sensitivity occurs because connections between neurons in the visual cortex are rearranged during development, and these cortical neurons become more responsive to the familiar pattern.  - If cats are exposed to a particular visual stimulus during the first few weeks of life (horizontal versus vertical lines), their ability to detect the previously exposed pattern is enhanced in adulthood. - This shift in sensitivity occurs because connections between neurons in the visual cortex are rearranged during development, and these cortical neurons become more responsive to the familiar pattern. - Sensitive periods have been shown in cognitive processes such as categorization, social competence, and communication. Compensatory Plasticity Hypothesis: - If sensory input (ex: vision, audition) is blocked during development, the functioning of that system may be blocked in adulthood. - Deficits in one sensory system may lead to enhanced ability in another sensory system. Chapman et al. (2010) - Guppies raised under different light intensities, then tested for how they responded to light or olfactory cues. - Fish raised under high light intensity respond better to visual stimuli, fish raised under low light respond better to olfactory cues. - Compensatory Plasticity Hypothesis: A loss or deficit in one sense results in heightened capacity in another. - Whereas natural selection is a slow process requiring many generations, compensatory plasticity allows animals to adapt, within their lifetime, to a new environment. In Summary: - Most animals do not have fully functioning sensory systems at birth. - Both normal development and fine tuning of sensory abilities depend on postnatal sensory experience. ○ Nature AND Nurture! 3 - Sensory System Function: - Two stages: ○ Sensory Detection: How animals acquire information about their sensory world. ○ Sensory Processing: How information is organized and transmitted to other brain regions. - Helps animals interpret the world around them, and respond appropriately. Sensory Detection: - Begins at the sense organs (eyes, ears, nose, skin, tongue), each of which  ○ Sensory Processing: How information is organized and transmitted to other brain regions. - Helps animals interpret the world around them, and respond appropriately. Sensory Detection: - Begins at the sense organs (eyes, ears, nose, skin, tongue), each of which contain sensory receptors. - Sensory receptors transmit info to Central Nervous System, through neuronal communication. - Action Potential: The transmission of an electrical signal from soma, along axon, to presynaptic terminal, resulting in release of neurotransmitters (neuron is “firing”) Transduction: - Sensory receptors respond not to neurotransmitter release, but to input from the environment. - This input arrives as a physical event (sound waves, light waves, airborne chemicals) - When these physical stimuli reach the sense organs, sensory receptors are activated and fire action potentials. - This process of taking this physical input and translating it into electrical signals/neuronal messages is called transduction. Sensory Processing: - Sensory information remains separated by modality as it is sent from the sense organs to the brain. - This is because there are separate neuronal pathways for vision, hearing, olfaction, etc. - This ensures that messages do not get “scrambled” as they are sent to the appropriate brain region. ○ Scent/taste most ancient ○ Visual system most complex Summary: - All cognitive processes are influenced at least initially by sensory input. - Sensory systems are the first point of contact between an organism and their environment. - While humans rely heavily on vision, other species have adapted to their respective environments. - Sensory information is transmitted to the central nervous system and on to different brain regions where is it processed and interpreted (ie: perception) Perception:  respective environments. - Sensory information is transmitted to the central nervous system and on to different brain regions where is it processed and interpreted (ie: perception) Perception: - Sensations: Produced when when physical stimuli activate sensory receptors, which then send neural circuits through specialized circuits. - Perception: The interpretation of these signals which occurs when sensory information is processed, organized, and filtered within the central nervous system. Psychophysics: - The study of the relationship between sensations and perception is called psychophysics. - Conducted by asking participant to indicate when they see a light, hear a sound, smell an odor, etc. ○ ex: hearing tests - BUT...animals can’t make verbal responses...so how do we test them? Psychophysics with Non-Human Animals: - Basically, we need to find a way to get a yes/no response from an animal. - The easiest way to do this is by training the animal to make one response when a stimulus is present (S+), and another response when the stimulus is not present (S-). Ernst Heinrich Weber: - German Physician - Noted that “in observing the disparity between things that are compared, we perceive not the difference between the things, but the ratio of this difference to the magnitude of things compared.” - In other words...we are able to distinguish the relative difference, not the absolute difference between items. Gustave Fechner: - German philosopher and scientist. - Concerned with how a person’s subjective experience could be measured scientifically. - Student of Weber; created formal equations based on Weber’s observations. Fechner's "3 Problems" of Psychophysics: - Detection: ○ Find a way to measure the minimum amount of a stimulus that could be detected (ie: absolute threshold).  - Student of Weber; created formal equations based on Weber’s observations. Fechner's "3 Problems" of Psychophysics: - Detection: ○ Find a way to measure the minimum amount of a stimulus that could be detected (ie: absolute threshold). - Discrimination: ○ Find way to determine how different two stimuli must be in order to be detected (ie: difference threshold/JND). - Scaling: ○ Find a way to describe the relationship between the intensity of the stimulus and the intensity of our sensation (ie: Fechner’s Law). Detection - Absolute Threshold: - Question: How much of an energy change, starting from zero, is required for a subject to sense it? - Below some level of intensity, a subject will not be able to detect it. As soon as the threshold intensity is exceeded, the subject can be expected to always detect it. This is known as the Absolute Threshold. - Absolute Threshold is not fixed! Psychometric Function: Dark Adaptation: - Dark adaptation is the lowered threshold for detecting light that occurs under reduced illumination. - Takes a few minutes to develop because it involves a series of neurochemical reactions in the eye. - Evolved in some humans and animals, providing ability to see during day and Dark Adaptation: - Dark adaptation is the lowered threshold for detecting light that occurs under reduced illumination. - Takes a few minutes to develop because it involves a series of neurochemical reactions in the eye. - Evolved in some humans and animals, providing ability to see during day and night. - Provides evidence that perceptions are not a direct reflection of sensations. Blough (1956) Birds in operant chamber must peck S+ if they detect light, and S- if they do not. Threshold to detect light is much lower the longer they are kept in a dark environment. Methodology: - What methods could we use to measure absolute threshold? 1. Method of Constant Stimuli 2. Method of Limits 3. Adaptive Testing Method of Constant Stimuli: - Uses a fixed number of stimuli of various intensities. - Each stimuli presented many times in different orders. - Subject response “yes” when stimuli is detected and “no” when it is not. - S-shaped curve is usually found for all sensory systems when using Method of Constant Stimuli. Method of Limits: - Focus only on stimuli near the absolute threshold - Descending series: Experimenter starts with easily detected stimuli, decreases intensity until subject can no longer perceive it. (Start above threshold, go down until stimulus not perceived) - Ascending series: Experimenter starts with stimuli that cannot be perceived, increases intensity until it can be perceived. (Start below threshold, go up until stimulus is perceived) Adaptive Testing (Staircase Procedure): - Method of limits only test stimuli that bracket the absolute threshold (the last two in the testing series)...all other stimuli in these sets tell us nothing. - Adaptive testing keeps the test stimuli “hovering” around threshold by adapting stimuli based on subjects responses. - Threshold is obtained by averaging stimulus intensity value of the reversals. Staircase Procedure: Signal Detection: - All of the detection methods we have talked about so far involve responses of “yes I perceive it” or “no I don’t perceive it”. - Problem—what if the individual wants to appear more sensitive than they really are? - Catch trials can help eliminate this problem...in these trials, no stimulus is presented. Signal Detection Theory: - Recognizes that any stimulus must be detected amongst a background of ongoing intermittent noise. - No absolute threshold, only a series of observations which must be categorized as ”signal present” or “signal absent” - Can be used to determine how sensitive individual is to a signal, independent of any expectation effects that might bias decisions. Outcome Matrix: Just Noticeable Difference: - JND is the amount by which two stimuli must differ so that the difference can be detected. - As the intensity of a stimulus increases, so does the intensity that produces a JND (ex: a dim light turned up in a dark room is immediately noticeable, Just Noticeable Difference: - JND is the amount by which two stimuli must differ so that the difference can be detected. - As the intensity of a stimulus increases, so does the intensity that produces a JND (ex: a dim light turned up in a dark room is immediately noticeable, whereas a much brighter light will need much more illumination to produce a perceptual change). - The ratio between the current stimulus intensity, and the intensity change required for a JND is called the Weber fraction. Weber's Law: - Weber's Law says that the size of the just noticeable difference (i.e., delta I) is a constant proportion of the original stimulus value. - Expressed as follows: 11I = k I ○ 11I is the difference threshold (or JND) ○ I is the intensity/magnitude of the standard ○ k is a constant, known as the Weber Fraction - The Weber fraction (k) is equal to 11I/I Difference Threshold (or JND) - Asks the question “by how much must two stimuli differ in order to be discriminated as not the same”. - We are still measuring a threshold, but in this case it is a threshold for the perception of a difference between the standard and comparison stimuli. - We can’t take the point where the comparison stimulus is considered “lighter” half the time and heavier half the time as a threshold—that is the point where the weights are judged to be the same (0.5 on y axis = 99g)...this is the point of subjective equality (PSE). - Instead, we are interested in the point where heavier/lighter can be distinguished from the PSE...this is the interval of uncertainty (0.25 and 0.75 on y axis).  half the time and heavier half the time as a threshold—that is the point where the weights are judged to be the same (0.5 on y axis = 99g)...this is the point of subjective equality (PSE). - Instead, we are interested in the point where heavier/lighter can be distinguished from the PSE...this is the interval of uncertainty (0.25 and 0.75 on y axis). Differences in Discriminative Ability: - Better discrimination = smaller difference threshold, and steeper curve Sensations Transformed to Perception: - Three Stages: ○ Sensory info segregated by modality (sound, light, etc.) ○ Sensory info coded for stimulus dimensions (duration/intensity) ○ Combined into a perceptual whole Sensations Transformed to Perception: - To understand how information is processed at each stage of the circuit, scientists implant electrodes in groups of neurons at each relay station and record how these neurons respond to different stimuli. - In the visual system, most of the sensory receptors in the eye project to a region of the thalamus called the lateral geniculate nucleus (LGN) LGN vs. Superior Colliculus: - Superior Colliculus is a visual pathway that does not travel through LGN. - 10% of retinal fibres project onto Superior Colliculus...was thought the be “vestigial” system. - LGN = the “what” of vision - Superior Colliculus = the “where” of vision - For this reason, cortically blind patients sometimes demonstrate “blindsight”  - 10% of retinal fibres project onto Superior Colliculus...was thought the be “vestigial” system. - LGN = the “what” of vision - Superior Colliculus = the “where” of vision - For this reason, cortically blind patients sometimes demonstrate “blindsight” and can tell you where an object is, even though they claim they cannot see it. Orbitofrontal Cortex: - Receives direct and indirect information from ALL sensory areas. - Likely has important role in sensory integration. - May help assign motivational significance, allowing animals to make decisions about how to react to stimuli - In sum, sensory processing occurs in stages with neurons responding to more and more complex aspects of the environment as information is transmitted to higher brain regions. Elemental Theories of Perception - Structuralism: - Discussed by Wundt (1832-1920) but mostly developed by Edward Titchener (1867-1927). - Theory holds that perceptions are created by combining or adding up elements of sensations. - Ex: For vision, visual stimuli are coded in different groups of neurons that convey this information, in parallel, to higher brain regions. When neural signals arrive at a new brain site, the information is recombined and transmitted to other parts of the brain. Feature Integration Theory: - The main evidence for structuralism stems from the fact that the time to process two features (ex: colour and shape) of a stimulus is the sum of the time it takes to process the two individually. - This effect would not be expected if perception was synergistic. - Feature Integration theory is a modern version of structuralism. It posits that elements of sensory input are coded at the initial stages of processing, and then combined at higher levels to produce perceptual wholes. Gestalt Psychology: - Elemental theories of perception seem at odds with human experience, in which the sensory world is perceived as “whole” - Gestalt psychologists proposed instead that individuals perceive sensory information in its entirety, and then divide in into elements if further processing is required. - Founded by Köhler, Wertheimer, and Koffka - Examples: