Perception, Planning and Action Sensory perception • Definitions. o Sensory Perception: process of obtaining information or knowledge (about the environment and the body) from sensory stimulation and making it available for doing things § About gaining knowledge § Is a process § Provides information for doing things • Extracting information, using mediums (e.g. light) o Doing things involves many processes § Communication, planning, decisions, memorising § The most important is the initiation and guidance of goal- directed motor behaviour (movement/action) • Organisms perceive in order to move o Has a purpose § A limited amount of behaviour can be carried out using non- perceptual sensory processes • This is reflex behaviour o Only uses senses, no perception o No information on the causes/source of the stimulation § Don’t know what caused it § Perception tells you about the causes of stimulation o Sensory perception is distinguished from other kinds of perception by: § The fact that it can provide info about the environment/body based on stimulation of the sensory organs § The primary source of info is immediately preceding stimulation of the sensory organs § It can operate without conscious experience (e.g. subliminal perception) § Other kinds of perception are active, conscious, CNS processes that aren’t based on immediate sensory stimulation • Meaning of stimulus o Reflex behaviours: involuntary elicited responses to proximal stimulation o Proximal Stimulus (stimulation): Physical energy or force (or properties thereof) that impinges on sensory receptors and evokes a change in their membrane potential. § Only require sensing, not perception § Some receptors only detect, go via passive induction § Others conduct APs o Perception involves obtaining info about the environment/body § Info about the distal stimuli (things/events in the world) § Distal Stimulus: An object, substance or event in the environment that is a source or cause of proximal stimulation and/or its characteristics • Perception is the process of obtaining info about distal stimuli from proximal stimuli o In visual perception proximal stimulation = the patterns of light intensity that are projected onto the retina(s) by the optics of the eye(s): the retinal image(s) • From stimulus to perception o Objects, surfaces, visible things all reflect light from various sources (distal stimuli) --determines→ pattern of light entering the eye that form retinal images (proximal stimuli) --stimulates→ photoreceptors transduce light into neural activity -- transformation/processing→ percepts: knowledge/info about distal stimuli • Vision contributes to behaviour o Visual info is used for: § Detection, identification, decision making, preparation of movement, initiation • Perceiving and moving o Organisms perceive so they can move § This is the primary reason why perception exists o To guide behaviour, you need relevant info at the right time, that isn’t contaminated by irrelevant info o Making info available means providing relevant info in a usable form § To acquire it you need the right proximal stimulation • Acquisition and processing need to be selective • Perceptual activities o Perception is an active process § Obtain/select relevant, uncontaminated info § Not passive reception of stimulation § 4 kinds of activities are involved: • 1) Information seeking activities: seek out (or generate) stimulation that contains the information required • 2) Information selection activities: select information needed for particular behaviour(s) from the total amount available o Proximal stimulation can contain lots of info, selected what is needed for the behaviour you engage in • 3) Enabling activities: establish a stable base that enables the sensory organs to operate effectively o Lets you extract info effectively • 4) Information extraction activities: process stimulation to extract useful information from it o These all involve behavioural components, except for 4 § Obtaining stimulation that contains useful info involves body movement • Move our sensory organs around o Neural processes involved in getting the info we need out of the stimulation/our sensory organs § Useful info extracted from the signals from sensory organs • Feeling: active touch o We use relevant sensory organs in specific ways, to obtain particular types of info o Active process, involves receptors in upper and deeper tissues § Touch used in everyday life is active/kinesthetic touch, or haptic perception § Activities that people use to obtain info have characteristic forms § There are 6 exploratory procedures • Hardness, weight, texture, shape, size, temperature • Smelling o Breathing in, but also motor activity § When dogs follow a scent trail, they move side to side • Humans can do the same, and weave as well o They improved with practice, and two nostrils are needed • Perceptual activities o Movement plays a role in our sense o We move our eyes/head/body when using retinas to obtain visual stimulation o Movement is needed to: § Obtain the stimulation needed to obtain required info § Keep the retinal images steady • Function of eye movements o Both eye movement and components of superordinate systems generate head and body movement § Some animals don’t make eye movements/have less capacity for making them, including some invertebrates amphibians, birds • They rely on head/body movement instead and use these to stabilise their eyes The Perceptual Process • Perceptual activities o Think of sensory organs as measuring instruments § Must be moved in specific ways, into the right position, and held in place • Without those, measurement would be impossible § Sensory organs are instruments for measuring variables of proximal stimulation • Some with routines/procedures (e.g. exploratory) • Sensory stimulation o Motor behaviour is part of perception - to obtain info o Other parts take place in the NS (the brain) § Getting info out of signals from stimulation o Perceptual activities are involved in getting stimulation § Processing is needed to get the info out • Visual perception o Takes the form of images projected onto the retinas (retinal images) § On the back of the eye § Light reflected off objects→ back of the eye→ optics forms image on the retina o Visual processing can be seen as solving a problem, roughly as follows: § From a 2D pattern of light projected onto the retinas, extract information about the location and motion (in 3D), properties and identity of objects and surfaces that is accurate enough to support normal behaviour in the world • Just given a 2D pattern of light intensity • This is difficult to solve o The nature of the stimulation is: § No depth in images § Image size depends on viewing distance • Objects of different size can project similar sized images § Shape of the image depends on the direction it’s viewed from, so it varies and is not the same as the real shape • Visual ambiguity o The same image could have been produced from infinite possible objects of different sizes/shapes/distances § Also, a single object can project many different images o Somehow our NS can resolve this ambiguity § Determine what the objects are where regardless of viewer’s location • How: not all logical possibilities are physically/ecologically likely o The world has rules and constraints • Resolving ambiguity o Know what’s impossible/unlikely → exclude possibilities § This is the basic principle of perceptual processes • The a priori knowledge comes from genetic inheritance and from experience o We start with poor perception and it improves with practice o If the only possibility that’s compatible with prior knowledge is wrong, then the percept is wrong § If something is in one place, then another, we perceive movement • E.g. films (many still images in a row with blanks in between) • Brain creates movement • Perceptual illusions o When the percept is wrong like this, a perceptual illusion occurs § Doesn’t represent the truth o Defining perceptual illusion (attempt): a consistent and persistent discrepancy between the perceived and real physical properties of a stimulus. Illusions are consistent in the sense that they invariably occur when the particular stimulus is presented and persistent in the sense that they are strongly resistant to efforts to suppress them. § But not every discrepancy is an illusion • Sometimes we just can't perceive something (for example if it only shows in UV light) • Only distal stimuli properties that our senses can detect should be defined as illusions o Perceptual illusion: a consistent and persistent discrepancy between a sensory percept and the distal stimulus that evoked the percept (and that the percept represents) such that the observer is deceived as to the nature of the distal stimulus. The discrepancy relates only to those (distal) stimulus properties which can be detected by the sensory systems and it occurs as a result of the normal processing of proximal stimulation. § Visual illusion: due to visual processing in the nervous system (internal) § Optical illusion: due to the physical nature of light travelling between transparent media (external) o In an illusion caused by small movements of the eye, it counts as an illusion because the NS has interpreted the retinal image motion from the eye movements as due to motion in the world (the distal stimulus) rather than motion of the image on the retina (proximal stimulus) • Resolving ambiguity o Perceptual illusions are due to the way perceptual processes work § Reflect the way prior knowledge is used to extract info