Sensory Processes PDF

SENSORY PROCESSES Course of Experimental Psychology Università Cattolica del Sacro Cuore Milan CLAUDIA REPETTO  TOC  Definitions of sensation and perception  Psychophysics  Vision  Audition  Olfaction  Gustation  Touch Pressure and pain ...

SENSORY PROCESSES Course of Experimental Psychology Università Cattolica del Sacro Cuore Milan CLAUDIA REPETTO  TOC  Definitions of sensation and perception  Psychophysics  Vision  Audition  Olfaction  Gustation  Touch Pressure and pain  Some definitions…  Sensation = activation of sense organs, stimulated by a source of physical energy  Perception = constructive process by which stimuli coming from the environment are elaborated and result in a meaningful unit  Stimulus = any passing source of physical energy that produces a response in a sense organ  Psycophysics = science studying the relationships between the physical features of the stimuli and the correspondent psychological experience  PSYCHOPHYSICS FIRE STIMULUS SENSATION PERCEPTION  Some more definitions…  Absolute threshold= the smallest intensity of the stimulus that must be present for it to be detected It is the boundary between what we are able to detect and what we cannot detect, even if it is present in the world It corresponds to the stimulus intensity that is detected in 50% of the cases Sometimes, noise (background stimulation that can involve different senses), may interfere with stimulus sensation  Some more definitions…  Difference threshold= the smallest intensity change needed to detect a difference between two stimuli (Just Noticeable Difference – JND) Can you see the difference between the two?  The new psychophysics Role of the individuals→ they are not passive receivers... 1. They evaluate and estimate the stimulus 2. They adapt their sensation to the environment 3. They decide whether or not to report the difference detected  The new psychophysics Role of the individuals→ they are not passive receivers... STEVENS’ LAW He had subjects do an estimate of 1. They evaluate magnitude and discovered that the relationship between sensory judgment and estimate and the intensity of the stimulus is a the stimulus power function Ψ= 𝚽𝒓 r1 →Ψ increases faster and faster compared to the physical magnitude  The new psychophysics Role of the individuals→ they are not passive receivers... SENSORY ADAPTATION Phenomenon in which 2. They adapt their the sensory capacity sensation to the decreases with long environment exposure to the same stimulus  The new psychophysics Role of the individuals→ they are not passive receivers... SIGNAL DETECTION 3. They decide It considers the influence of the whether or not to subject's decision-making on the report the presence or absence of a difference detected stimulus HIT – FA – O –CR Influenced by: - Sensitivity - Personal attitudes VISION Image formation  The image-forming system itself consists of the cornea, the pupil, and the lens  The cornea is the transparent front surface of the eye  The lens focuses the light on the retina  So, light reflected from an object forms an image of the object on the retina  Based purely on optical considerations we can infer that the retinal image is inverted Two types of receptor cells CONES → light sensitive, responsible for detailed focus, color perception, particularly in bright light situations Two types of receptor cells RODS→ thin and cylindrical, highly sensitive to light, they are activated in low light conditions and lead to low-resolution, colorless sensations A schematic picture of the retina The bipolar cells receive signals from one or more receptors and transmit those signals to the ganglion cells, whose axons form the optic nerve The role of the fovea  When we want to see the details of an object, we routinely move our eyes so that the object is projected onto the fovea.  On the fovea the receptors are plentiful and closely packed → higher resolution  Form the eye to the brain  Photoreceptors are hit by the electromagnetic wave → some chemicals change in composition and trigger a neural response (trandusction)  Bipolar cells → they receive information directly from rods and cones and communicate this information to ganglion cells  Ganglion cells → they collect and synthesize visual information, which is then sent from the back of the eyeball to the brain through a bundle of ganglion axons called the optic nerve  Let’s try our blind spot! The blind spot is the area where the optic nerve leaves the eye, so it has no receptors. Close the left eye and fix the black point with the right one. Move the page away and closer until the car disappears from your view: it ended up in the blind spot! Optic chiasm: point of conjunction between the two optic nerves, where they cross before starting their way to the brain Primary visual area (BA 17): located in the occipital lobe, in correspondence with the calcarine fissure. The visual field representations are crossed. Here the extraction of the characteristics takes place  Features extraction In the visual cortices there are specialized cells for the detection of lines oriented in a certain way (single-cell recording)  Features extraction … or other specific characteristics of the stimulus, which are processed in parallel The visual message into the brain  Two ways OPTICAL ATAXIA Ventral way: occipital lobe → temporal lobe. Dedicated to the perception of the attributes of an object, such as shape, size and orientation useful for its recognition (what an object is). Dorsal way: occipital lobe→ parietal lobe. It analyzes the position of objects in space (where an object is)  Two ways Ventral way: occipital lobe → temporal lobe. Dedicated to the perception of the attributes of an object, such as shape, size and orientation useful for its recognition (what an object is). Dorsal way: occipital lobe→ VISUAL parietal lobe. It analyzes the AGNOSIA position of objects in space (where an object is)  Color: it’s a matter of wavelength Frequency Infrared Ultraviolet Radio Television Microwave X-rays 𝜸 − 𝒓𝒂𝒚𝒔 Wavelenght 400 nm 750 nm  Color appearance Hue: quality described by the name Brightness: how much light is reflected Saturation: purity of the color  Theories of color vision TRICHROMATIC THEORY There are 3 types of cones, each of which responds preferentially to a range of wavelength (blue/violet; green; yellow/red).  Color blindness Genetic disorder that determines the inability to see the red or green color. It supports the trichromatic hypothesis  THE COLOR TRICHROMATIC OPPONENT COLOR THEORY THEORY The receptors are linked in There are 3 types of pairs and work in opposition to each other (yellow-blue; cones, each of which red-green; white-black). responds When one component is preferentially to a overstimulated (i.e. red), than it becomes fatigued range of wavelength and the other component (blue/violet; green; comes into play (i.e. green) yellow/red).  Complementary afterimages  http://i.imgur.com/CGyFe05.gif AUDITION  The ear: structure and function Sound = movement of air molecules caused by a source of vibration It enters from the outer ear, proceeds inside the auditory canal and reaches the eardrum = taut membrane that vibrates with the passage of sound  The ear: structure and function  From here the vibrations pass to the middle ear = small cavity that contains three small bones (malleus, incus and stapes) that transmit the vibrations to the oval window  The ear: structure and function The internal ear transforms sound into energy to be sent to the brain. It also contains the organs that allow us to locate the position of the body and to move in space  The ear: structure and function Cochlea = spiral-shaped tube similar in appearance to that of a snail and containing a fluid capable of vibrating in response to sound Basilar Membrane = structure that crosses the central part of the cochlea dividing it into an upper and a lower cavity Hair cells= if moved by the vibrations entering the cochlea, they send a neural message to the brain From the ear to the brain  Sound features Frequency number of complete vibrations that occur in one second → Pitch, quality that defines a sound as high or low Amplitude Pressure difference between the peak and the trough → Loudness, measured in decibels  Sound localization Since we have two ears, the sound arrives first at one of the two and allows us to locate the source. The head acts as a partial barrier  Sound theories RESONANCE – TEMPORAL THEORY PLACE THEORY The sound wave causes the entire basilar Different areas of membrane to vibrate, the basilar and the rate of membrane respond vibration determines to different types of the rate of impulses of frequencies. nerve fibers in the auditory nerve  EQUILIBRIUM Semicircular Canals = three tubes containing a liquid that moves inside them when the head moves, signaling a rotational or angular movement to the brain Otoliths = crystals that signal forward, backward, up and down movements, along with the force of gravity  OLFACTION The sense of smell is able to:  discern between more than 10,000 different smells  identify sex by smell  evoke memories OLFACTION The molecules of a substance enter the nasal canal and meet the olfactory cells. Through the nerve fibers the signal reaches the olfactory bulb, located under the frontal lobes and connected with the olfactory cortex, inside of the temporal lobes (link with memory system)  GUSTATION It is the sense that allows the qualitative evaluation BITTER of a substance based on flavor SOUR The receptive cells are the taste buds, they are about 10,000 and are SALT distributed between the SWEET tongue and other parts of the mouth and throat Supertasters vs Nontasters  TOUCH On each cm of skin there are 130 different types of tactile receptors Three kinds of somatic sensitivities: 1. Meccanoceptive (pressure) 2. Thermal (temperature) 3. Dolorific (pain)  Phantom Limb  https://www.youtube.com/watch?v=1mHIv5ToMTM  Pain  It has an evolutionary protection function  It arises following a variety of stimuli  It can be phasic (sharp, brief in duration) or tonic (dull and long-lasting)  It is largely influenced by factors unrelated to the intensity of the painful stimulus, and linked to emotional evaluation  “Gate control” theory Specific receptors in the spinal cord are connected to certain areas of the brain related to the sense of pain. When the receptors are activated, they open a gate and the sensation of pain is experienced The gate can be closed in two ways Competition Psychological between stimuli factors  Pain reduction: the distraction method  Wounded American soldiers report a reduction in pain and an increase in comfort during medication if they undergo a Virtual Reality session in the Snow World environment at the same time as medical procedures (Hoffman, 2003 and following) https://www.youtube.com/watch?v=jNIqyyypojg