Motion Perception PDF

# Motion Perception ## Functions of motion perception - Motion captures attention, facilitating the perception of an object. - Motion provides information about objects and helps separate the object from the background. ## What if we can't perceive Motion? - Difficulties when pouring a liquid. -...

# Motion Perception ## Functions of motion perception - Motion captures attention, facilitating the perception of an object. - Motion provides information about objects and helps separate the object from the background. ## What if we can't perceive Motion? - Difficulties when pouring a liquid. - Inability to see series/films. - Serious difficulties in dialogue and understanding emotion. - Higher risk of getting knocked down. ## Sensitivity to detect motion in humans - The smaller the object that moves is the easier it is to detect it. - As movement perception decreases, the IQ increases (for big stimuli) since intelligent people tend to suppress peripheral information attempting to focus on the important. ## The Influence of Context - The threshold to detect motion from a small object is from 1/6 to 1/3° per s when the context is homogenous. - When the context is vertical patterned and the stimulus moves horizontally, the threshold is 1/60° per s, our ability increases. ### Real and apparent motion - **Gestalt**: One thing is the elements and another is the whole. - The whole seems like it is moving but each element is moving in a straight line. - **Persistence of vision**: Result of successive afterimages, which are superimposed by the action of the mind, making us believe that what we see is a single object in motion. ## Real life application - Roads. ## Apparent motion - **Why?** Even though it's apparent motion, the mental mechanisms are the same as with real motion, particularly processing beyond the retina. ## We can also see like something is moving even if it is not due to a previous stimulation (buda) ### Stimuli - **do not move but...** - *Two stimuli in different locations alternate 30ms<IEE<200/300ms* - *Watching a moving stimulus causes motion perception of a stationary stimulus* - *A moving stimulus causes motion perception of a nearby stationary object* ### Stroboscopic movement - *Motion aftereffects*: The waterfall effect and the rotating spiral… - *Induced (or Motion) aftereffects*: Moon and clouds, trains, buses…. ## Perceiving biological motion - Perceiving motion of living things. - Before appreciating local properties (e.g., color of clothes), processed by the ventral pathways, we can identify someone just by the way they move. - This is due to how quickly the dorsal pathway is in our brain. - We are very sensitive to identifying living things just by the way they move. ## Optic flow - Movement of elements in the scene relative to the observer. - Visual information received when we are in movement at a certain speed, from a “hypothetical center”. - When it is random (created by a computer), we are not able to receive information. ### Gradient of flow - Differences in the speed of the optic flow as a function of distance from the observer (closer=faster), providing information about our speed. ### Focus of expansion - Point in the distance where there is no flow - the "hypothetical center." - They provide information about where we are heading. # Depth and Size Perception ## Types of Depth Cues - **Depth cues**: Indicate depth in an object or scene. Typically used implicitly and are visually learned. ### Oculomotor cues - **Accommodation of the Lens**: Fine motor muscles surrounding the lens change the lens shape to focus the object in order to make the image clear. - *Distance: relaxation = flat, up close: contraction = bulge* - The brain knows this is occurring by the messages sent by the muscles, which provides information about depth. - *Limitation: only two meters* - **Convergence of the eyes**: Fine motor alignment of the eye muscles, so that the line of sight of each eye points at the same object. - The brain can then fuse the images from each eye into a single image. - *Limitation: Only binocular (if not aligned, double image), only effective in less than 10 meters.* ### Pictural cues - Depth cues that are represented explicitly in two-dimensional pictures, indicating depth: - Occlusion (behind). - Perspective convergence. - Texture gradient. - Shadows. - Relative height. - Relative size. - Familiar size - typical size of objects. - Atmospheric Perspective (just in open spaces). ### Binocular retinal disparity - The distance between the eyes means that two different slightly different images are sent to the brain. - F, the eye fixation point, is the same but the other points are not correspondent. - The idea of "binocular retinal disparity" applies to all points in the scene located at a distance from the observer longer or shorter than F. - Points on the scene with no disparity are the points projected on corresponding points of the two retinas. - Points with disparity are the points projected on non-corresponding points of the two retinas. ## Humans have binocular disparity neurons in the striate cortex - These neurons respond best to a particular level of disparity, which provides information about where the objects are in the scene for the brain. ## Stereopsis: Perception of depth in objects or scene - Based on information provided by binocular disparity. - Particularly useful when very few cues are available. - Binocular disparity is a biological fact, but this is taking advantage of it. ### The two foveas - They are always corresponding points of the retina and are 0°. ### Stereoscopes and 3-D films - Force the depth taking advantage from the ability to perceive depth from binocular disparity. - However, if the images are too different, *binocular rivalry* occurs, where perception will be unstable, shifting between the two images. ## Difficulties in stereo vision - **4.5% lack binocular disparities** - Causes: *eyes are misaligned, not developing the needed neurons* - Consequences: *No 3D films, no normal appreciation of depth, problems in foggy weather, sports where the time of response with a moving object is impossible.* - About 68% have good to excellent stereo vision, whereas 32% have moderate to poor stereo vision. - This is likely to be reversible. A learning-based therapy can be used to exploit experience-dependent plastic mechanisms, which can be used to recover stereoscopic visual function in adults. - Patients with Alzheimer's disease are significantly impaired in the use of monocular and binocular depth cues. ## Additional depth cues in self-motion: motion-produced cues - This is a cue that we can only perceive in movement, not while being still. - **Motion parallax** is the imaginary movement of physical things in the world. It's the representation of the things in our retina moving. - *If things are close, they move in the opposite direction as we move.* - *If things are far, they move in the same direction as we move.* # Perceiving Object Size from Vision ## Visual angle - The angle of an object, relative to the observer's eye (to the center of the lens), determines both the physical size and the physical distance of the object. - *Physical size:* Bigger visual angle means a bigger object. - *Physical distance:* Bigger visual angle means closer object. ## The visual angle determines the retinal size of the object - The retina image has a given size, but it needs more than the retinal size of the object since objects at certain distances from the observer can produce the same visual angle. ## The brain takes into account two different factors: size constancy and the perceived distance at which objects are - **Size constancy:** When changing the distance of an object, we do not notice any change in the perceived size of the object. This is provided when one of these circumstances are met: - *The object is known and their size too.* - *The observer perceives the changes in distance and notices the object is at half of the distance below.* - **What if the object size is unknown and it's hard to perceive the distance?** - Ex. *The Ames room* - **Holway and Boring-1941**: Participants had to adjust the diameter of the comparison circle to match the size of the test circle - the perceived distance: - *Case 1 (binocular+no visual restriction) almost perfect* - *Case 2 (monocular+no visual restriction) almost perfect* - *Case 3 (monocular+peepholes) loss of pictorial cues - very far from the correct performance* - *Case 4 (monocular+peephole+drapes) no cues of depth - worst scenario* ### Size-distance scaling mechanism - S=K (RXD) - **R**: retinal size, **D**: perceived size - We can predict what depth the brain will perceive. ## It can also explain the change in afterimages when the perceived distance varies - **EMMERT's law** - The retinal image is the same because it is an afterimage. - However, in real life situations, familiar objects at a large distance appear microscopic. - **Gibson's ecological approach to perception**: We should study this in a natural environment, not in labs, prioritizing the reality. - There are other sources of information that also contribute to size perception, such as relative size and textures. - His theory is that retinal size is not as important as long as our vision is good and we can perceive distance (direct approach to perception). ## Muller-Lyer illusion: - **Illusion**: When we have a tendency to perceive something that is not there or we perceive it differently (which exceeds the normal levels of subjection). - We are adding (top-down processing) automatically. # Auditory Perception - We perceive different sounds depending on the loudness, pitch, and timbre due to the waves (molecules on the air move = sound). ## The stimulus in auditory perception: sound as pressure changes - We automatically perceive the changes in the pressure (increase = condensation, decrease = rarefaction). - The molecules in the air or water move and create waves, which lets us know their particular physical features. - **Period**: From 0 level to 0 level (cycles/sec or Hertz): ## Pure and complex tones - **Pure tone**: Only one frequency, one wave. - **White noise**: A mix of frequencies in the same proportion. - **Complex tone**: The dominating pure tone (fundamental frequency), strongly related to the pitch we hear, combined with frequencies multiple of the fundamental. - **Fourier analysis**: Mathematical analysis that allows us to detect different pure tones forming a sound when applied to sounds. ## Sounds as a perceptual experience ### Pitch - Mostly associated with sound frequency. - Lower pitch = Less frequent - Higher pitch = More frequent ### Loudness - Associated with sound level. - Higher sound level = Louder sound ### Phons - Using Stevens techniques, we can estimate an individual's perception. - This gives us a model where the participant is going to estimate the magnitude of their perception. - It serves for the all curve, not only for the given point. - **Two equal loudness curves (ELC)**: - *The audibility curve (thresholds): phons = 0* - *The ELC of pain thresholds: phons > 120* ### The audibility threshold - Contains the minimum we need to detect a sound. ### Timbre - It lets us identify different instruments when the other characteristics are the same (compared to the color). - Harmonics determine the timber. # The Auditory System, Pitch Perception, and Auditory Masking ## Outer ear - Noise enters the auricle and then the auditory canal, where it is found by the tympanic membrane. ## Middle ear - Three little bones: malleus, incus, and stapes. ## Inner ear - Cochlea, connected to semicircular canals. - Sound reaches the ear canal as vibrations of air (unless underwater), vibrating the tympanic membrane, then vibrating the middle ear. - The stapes vibrates and the liquids inside of the cochlea vibrate, causing changes within the inner ear. - The organ of Corti contains inner cells that transduce the vibrations of the liquids into electric energy. ## Békéys' Place Theory of Hearing - The representation of frequency in the cochlea. - The frequency of a sound is indicated by the place along the cochlea at which the response is highest. - Sounds make the basilar membrane vibrate. The vibrating motion of the basilar membrane is a traveling wave. The picks are different places depending on the frequency of the sound. - **Tonotopic map of the chochlea:** - **Apex (inner part)** responds best to low frequencies. - **Base** responds best to high frequencies. ### How can sound vibrations in the era lead to perception of differences in pitch? - The cochlea automatically breaks down complex tones into their component frequencies. - It performs **Fourier Analysis**. - **Cochlear implants** can bypass damaged hair cells. They consist of: - A *microphone* (behind the ear). - A *sound processor* (behind the ear). - A *transmitter* (behind the ear). - A *receiver* surgically mounted on the mastoid bone. - *Electrodes* inserted into the cochlea to electrically stimulate auditory nerve fibers. ## Even if we block the auditory canal, vibrations are still received by our skull (direct to the cochlea) # Auditory areas in the cortex - The first area from the brain to receive information from the ears is the auditory cortex in the temporal lobe where it is separated into 2 pathways (*where* and *what*). - **Music training shows enlargement in auditory cortices.** # Hearing loss - **I. Conductive hearing loss - Damage in the outer or middle ear:** Fluid in the middle ear from colds, ear infection, allergies, poor eustachian tube function, perforated eardrum, benign tumors, impacted earwax (cerumen), infection in the ear canal, presence of a foreign body, absence or malformation of the outer ear, ear canal, or middle ear. - **II. Sensorineural loss - Damage in the inner ear or the auditory nerve:** Illnesses, drugs that are toxic to hearing, hearing loss that runs in the family, aging, head trauma, malformation of the inner ear, exposure to loud noise. - **III. Mixed hearing loss - A conductive hearing loss in combination with a sensorineural hearing loss:** ~29 # Sound localization: Ability to know where a sound is coming from in space (without using the eyes) - **Auditory space**: Sounds that are around us at a given moment, coming from different places. We can locate them individually even though there are multiple sounds. - **Three dimensions**: - *Azimuth: horizontal* - *Elevation: vertical* - *Distance from observer* - A tester made with 227 loudspeakers asked where the sound comes from. ### Localization of sounds along the azimuth - Sounds directly in front of us are best located, easier to detect. - Two main binaural cues to the brain to know where it is, depending on the two ears (which one they reach before and physical intensity). ### Internal time difference (ITD) - For sounds in front of or behind the listener, ITD = 0 (arrives at the same time). - For sounds off to the side, ITD is greater than 0. - This clue is particularly effective in low-frequency sounds. ### Interaural level difference (ILD) - For sounds in front of or behind the listener, ILD = 0 because the sound level is the same for the two ears. - For sounds off to the side, ILD > 0, because the sound reaching one of the ears is attenuated by the head, which acts as an acoustical shadow. - This cue is particularly effective in high-frequency sounds because the head imposes obstacle. - The lower the frequency, the smaller the ILD = *poor localization*. - The higher the frequency, the greater the ILD = *good localization*. - However, at a given moment, there are points in the environment that produce virtually the same ITD and ILD. - **The cone of confusion**: A hypothetical cone-shaped surface in the auditory space, which contains the points of the auditory space that have highly similar ITD and ILD. We are bad at localizing the sounds coming from these points. # Perceptually Organizing Sounds in the Environment - **Auditory scene**: The array of sound sources in the environment at a given moment (*what they mean*). - **Auditory scene anlaysis**: The brain separates the sound sources from all of the other sounds in the auditory scene at a given moment, so we can perceive those sounds in the sound background. - **Principles of auditory grouping**: - *Location*: Sounds that are close tend to be perceived as a group. - *Similarity of timbre and pitch.* - *Proximity in time*: If we receive sounds without enough separation time, we only hear one (or a mix/masking). - *Auditory continuity*: Sometimes we are unable to perceive separations. - *Experience: Schema.* ## The case of hearing inside rooms: Indirect (reflected) sounds - When we are inside, most sounds reach our ears after reflecting off of the walls and other surfaces (some of it being absorbed, creating reflected sounds). - Different sounds coming from different points (direct and various indirect). - How does our brain solve this problem? Our brain can solve this if the interval in time is short because we group them.