8.1 Apparent motion
9 min read•august 20, 2024
Apparent motion is a fascinating aspect of visual perception where our brains create the illusion of movement from static images. This phenomenon is crucial for understanding how we process visual information and interpret the world around us.
The topic covers various types of apparent motion, including and . It also explores factors that influence our perception of motion, such as spatial and , and the biological significance of this ability.
Apparent motion
- Apparent motion is the perception of motion created by rapidly presenting a series of static images in succession
- It is a fundamental aspect of visual perception that allows us to perceive motion in the absence of physical movement
- Apparent motion is crucial for understanding how the brain processes and interprets visual information to create a coherent perception of the world
Phi phenomenon
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- The phi phenomenon is a type of apparent motion where a series of stationary stimuli presented in rapid succession creates the illusion of
- It occurs when the stimuli are presented at a specific spatial and temporal frequency, causing the brain to fill in the gaps between the stimuli and perceive a smooth, uninterrupted motion
- The phi phenomenon is often demonstrated using a series of flashing lights or dots that appear to move in a particular direction when presented at the appropriate frequency
Beta movement
- Beta movement is another type of apparent motion that occurs when two or more stimuli are alternately presented at different locations
- Unlike the phi phenomenon, beta movement does not create the illusion of continuous motion but rather the perception of a single object moving back and forth between the stimulus locations
- Beta movement is often used in experimental settings to study the factors that influence the perception of apparent motion, such as the distance between stimuli and the timing of their presentation
Biological significance of apparent motion
- The perception of apparent motion has significant biological implications, as it allows organisms to detect and respond to moving objects in their environment
- In the wild, the ability to perceive motion is crucial for survival, enabling animals to detect predators, track prey, and navigate their surroundings
- In humans, the perception of apparent motion is essential for tasks such as driving, playing sports, and interpreting body language and facial expressions
Factors affecting apparent motion
- Several factors can influence the perception of apparent motion, including the spatial and temporal characteristics of the stimuli, as well as the observer's attention and prior experience
- The distance between stimuli, known as , plays a crucial role in determining whether apparent motion is perceived
- The timing of stimulus presentation, or temporal frequency, also affects the perception of apparent motion, with higher frequencies generally producing smoother and more convincing motion illusions
Spatial frequency
- Spatial frequency refers to the number of cycles of a repeating pattern within a given space, typically measured in cycles per degree of visual angle
- In the context of apparent motion, spatial frequency describes the distance between the stimuli used to create the motion illusion
- Lower spatial frequencies (i.e., larger distances between stimuli) tend to produce more compelling apparent motion, while higher spatial frequencies may result in the perception of flickering or pulsating stimuli
Temporal frequency
- Temporal frequency refers to the number of times a stimulus is presented within a given time period, usually measured in cycles per second or Hertz (Hz)
- The temporal frequency of stimulus presentation is a critical factor in determining the quality and convincingness of apparent motion
- Higher temporal frequencies generally produce smoother and more continuous motion, while lower frequencies may result in the perception of discrete, stuttering movements
Korte's laws
- are a set of principles that describe the relationship between the spatial and temporal characteristics of stimuli and the perception of apparent motion
- The laws state that the optimal conditions for perceiving apparent motion occur when:
- The distance between stimuli is relatively small
- The time interval between stimulus presentations is short
- The intensity or salience of the stimuli is high
- These principles highlight the importance of both spatial and temporal factors in creating compelling motion illusions
Stimulus onset asynchrony (SOA)
- refers to the time interval between the onset of one stimulus and the onset of the next stimulus in a sequence
- SOA is a critical factor in determining the perception of apparent motion, as it influences the temporal frequency of stimulus presentation
- Shorter SOAs tend to produce more convincing motion illusions, while longer SOAs may result in the perception of discrete, unrelated stimuli
Interstimulus interval (ISI)
- is the time between the offset of one stimulus and the onset of the next stimulus in a sequence
- Like SOA, ISI plays a crucial role in the perception of apparent motion, as it contributes to the overall temporal frequency of stimulus presentation
- Shorter ISIs generally produce smoother and more continuous motion, while longer ISIs may disrupt the illusion of motion and result in the perception of separate, static stimuli
Stroboscopic vs continuous motion
- refers to apparent motion created by presenting a series of discrete, static images in rapid succession, similar to the frames of a movie or animation
- Continuous motion, on the other hand, involves the presentation of a smoothly moving stimulus without any interruptions or gaps
- While both stroboscopic and continuous motion can create the illusion of movement, stroboscopic motion relies on the brain's ability to fill in the gaps between the discrete images, while continuous motion provides a more direct representation of motion
Long-range vs short-range apparent motion
- refers to the perception of motion over relatively large distances, typically spanning several degrees of visual angle
- , in contrast, occurs over smaller distances, usually within a single degree of visual angle
- The distinction between long-range and short-range apparent motion is thought to reflect different underlying neural mechanisms, with long-range motion processing involving higher-level cortical areas and short-range motion relying on more local, low-level motion detectors
Attentional modulation of apparent motion
- Attention can significantly influence the perception of apparent motion, with focused attention enhancing the salience and convincingness of motion illusions
- When observers direct their attention to the stimuli used in an apparent motion display, they are more likely to perceive a compelling sense of motion compared to when their attention is divided or directed elsewhere
- This highlights the role of top-down cognitive processes in shaping our perception of the world
Neural mechanisms of apparent motion
- The perception of apparent motion arises from the activity of specialized motion-sensitive neurons in the visual cortex
- These neurons, known as motion detectors, are tuned to respond to specific patterns of spatiotemporal change in the visual input
- The activity of motion detectors is thought to underlie the perception of both real and , with the integration of their outputs giving rise to the conscious experience of movement
Motion detectors in visual cortex
- Motion detectors are found in several areas of the visual cortex, including the primary visual cortex (V1), middle temporal area (MT/V5), and medial superior temporal area (MST)
- V1 contains simple motion detectors that respond to local, directional changes in the visual input, while MT and MST house more complex motion detectors that integrate information over larger spatial scales and are sensitive to global motion patterns
- The hierarchical organization of motion processing in the visual cortex allows for the extraction of increasingly abstract and sophisticated motion signals, culminating in the perception of coherent, meaningful motion
Magnocellular vs parvocellular pathways
- The visual system comprises two main processing streams: the magnocellular (M) and parvocellular (P) pathways
- The M pathway is specialized for processing motion, depth, and low-contrast information, and is thought to be primarily responsible for the perception of apparent motion
- The P pathway, in contrast, is more sensitive to color, fine detail, and high-contrast information, and is less involved in motion processing
- The differential contributions of the M and P pathways to motion perception highlight the specialized nature of visual processing in the brain
Illusory motion
- Illusory motion refers to the perception of motion in the absence of any physical movement of the stimulus
- Various types of illusory motion have been documented, including , , and the
- These illusions arise from the brain's interpretation of ambiguous or conflicting visual information, and provide valuable insights into the mechanisms underlying motion perception
Induced motion
- Induced motion is a type of illusory motion in which the perceived motion of a stationary object is influenced by the movement of nearby objects
- For example, when a stationary target is surrounded by a moving background, the target may appear to move in the opposite direction to the background
- Induced motion demonstrates the role of contextual information in shaping our perception of motion, and highlights the brain's tendency to interpret visual input in a coherent, unified manner
Autokinetic effect
- The autokinetic effect is an illusory motion phenomenon in which a stationary point of light viewed in complete darkness appears to move or drift erratically
- This illusion is thought to arise from small, involuntary eye movements that cause the retinal image of the light to shift, creating the impression of motion
- The autokinetic effect illustrates the importance of stable visual reference frames in maintaining accurate spatial perception, and shows how the brain can be misled in the absence of reliable contextual information
Motion aftereffects
- Motion aftereffects (MAEs) are a type of illusory motion that occurs after prolonged exposure to a moving stimulus
- After viewing a stimulus moving in one direction for an extended period, a subsequently viewed stationary stimulus will appear to move in the opposite direction
- MAEs are thought to reflect the adaptation of motion-sensitive neurons in the visual cortex, which become temporarily biased towards the opposite direction of motion after prolonged stimulation
Waterfall illusion
- The is a well-known example of a motion aftereffect, named after the observation that stationary rocks appear to move upward after watching a waterfall for an extended period
- This illusion demonstrates the powerful influence of prior sensory experience on subsequent perception, and provides evidence for the existence of specialized motion detectors in the visual system
- The waterfall illusion and other MAEs offer valuable tools for studying the adaptive properties of motion processing in the brain
Apparent motion in depth
- Apparent motion can also be perceived in depth, creating the illusion of objects moving towards or away from the observer
- This type of apparent motion relies on the brain's interpretation of binocular disparity cues, which arise from the slightly different views of the world seen by the left and right eyes
- The perception of motion in depth is crucial for navigating the environment and interacting with objects, and is thought to involve specialized neural mechanisms in the visual cortex
Ternus-Pikler display
- The is a type of apparent motion illusion that demonstrates the role of perceptual grouping in motion processing
- In this display, three aligned elements are presented in alternation with a shifted version of the same elements, creating the perception of either element motion (short-range) or group motion (long-range) depending on the timing of the alternations
- The Ternus-Pikler display highlights the brain's tendency to organize visual input into coherent, meaningful groups, and shows how this grouping process can influence the perception of motion
Transformational apparent motion
- is a type of apparent motion in which the perceived motion is accompanied by changes in the shape, size, or other properties of the stimuli
- This type of motion can create compelling illusions of objects deforming, expanding, or contracting as they move, and is thought to rely on high-level motion processing mechanisms in the visual cortex
- Transformational apparent motion demonstrates the brain's ability to integrate multiple sources of visual information to create a coherent, dynamic representation of the world, and highlights the complex nature of motion perception in the human visual system
Key Terms to Review (23)
Apparent motion in depth: Apparent motion in depth refers to the perception of movement through three-dimensional space based on visual cues, leading observers to interpret stationary objects as if they are moving in a specific direction. This phenomenon occurs when certain visual stimuli create the illusion of depth, giving rise to dynamic interactions between objects and the viewer's perspective. It can be influenced by various factors such as motion parallax, stereopsis, and convergence, all of which contribute to how we perceive movement within our environment.
Attentional modulation of apparent motion: Attentional modulation of apparent motion refers to the phenomenon where the perception of motion in static images can be influenced by the viewer's focus and attention. This modulation occurs because the brain integrates information over time, and when attention is directed toward certain elements, it can alter how motion is perceived, leading to changes in the apparent speed or direction of moving objects.
Autokinetic effect: The autokinetic effect is a visual phenomenon where a stationary point of light in a dark environment appears to move. This effect occurs due to the lack of external reference points, causing the observer's eyes to make small involuntary movements, leading to the perception of motion. This phenomenon highlights how our perception can be influenced by context and the absence of visual cues.
Beta Movement: Beta movement is the perceptual phenomenon where an observer perceives continuous motion between two or more stationary images that are presented in quick succession. This effect is crucial in understanding how our visual system constructs motion perception, emphasizing the brain's role in filling in gaps between visual stimuli to create a seamless experience of movement.
Continuous motion: Continuous motion refers to the perception of movement that occurs without interruption or pause, creating a fluid experience in visual processing. This concept is closely tied to how our brains interpret successive images or stimuli over time, allowing us to perceive movement as a seamless flow rather than a series of disconnected snapshots. This plays a critical role in understanding how we perceive apparent motion, where still images are perceived as moving due to the timing and arrangement of visual stimuli.
Illusory motion: Illusory motion refers to the perception of movement in a static image or scene, where observers perceive motion that is not physically present. This phenomenon occurs when certain visual cues, such as changing patterns, sequences, or spatial arrangements, trick the brain into interpreting these cues as motion. Illusory motion plays a significant role in understanding how our brains process visual stimuli and interpret dynamic scenes.
Induced motion: Induced motion refers to the perception that a stationary object appears to move when the background or surrounding objects are in motion. This phenomenon illustrates how our perception of movement can be influenced by context and is closely tied to understanding how we perceive motion, including apparent motion, motion detection, and motion integration.
Interstimulus interval (isi): The interstimulus interval (isi) refers to the time duration between two consecutive stimuli presented to a subject. This timing can significantly influence the perception of motion and the ability to detect changes in visual stimuli. A well-timed isi can create a sense of apparent motion, where stationary objects seem to move due to their sequential presentation.
Korte's Laws: Korte's Laws describe the principles governing the perception of apparent motion, particularly in how we perceive two or more stationary objects moving in a sequential manner. These laws help explain why we perceive motion between objects that are actually at rest, emphasizing the importance of temporal and spatial factors in our visual perception system.
Long-range apparent motion: Long-range apparent motion refers to the perception of movement that occurs when two or more stationary objects are viewed in succession, creating the illusion that one object is moving across a greater distance than it actually is. This phenomenon highlights how our brain interprets visual stimuli over larger spatial areas, influencing our understanding of motion in dynamic environments.
Magnocellular vs Parvocellular Pathways: The magnocellular and parvocellular pathways are two distinct neural pathways in the visual system, crucial for processing different aspects of visual information. The magnocellular pathway is primarily responsible for motion detection and processing visual information related to dynamic changes, while the parvocellular pathway focuses on color, fine detail, and texture recognition. Understanding these pathways helps clarify how we perceive motion, including apparent motion.
Motion aftereffects: Motion aftereffects refer to the optical illusion that occurs when a person perceives motion in a stationary object after being exposed to moving stimuli. This phenomenon highlights the brain's adaptation to motion, leading to a perceived shift in stationary objects in the opposite direction of the previous movement. The experience can provide insights into how we detect motion and how visual perception adapts over time.
Motion detectors in visual cortex: Motion detectors in the visual cortex are specialized neurons that respond to the movement of objects within the visual field. These neurons play a critical role in processing motion information, helping us perceive dynamic scenes and navigate through our environment. By detecting changes in position over time, they contribute to our understanding of motion, depth, and directionality in visual perception.
Neural mechanisms of apparent motion: Neural mechanisms of apparent motion refer to the brain's processes that allow it to perceive motion when no actual movement occurs, such as when two stationary lights blink on and off in succession. This phenomenon relies on various neural pathways and areas in the brain, such as the visual cortex, to interpret the sequence of events and create the illusion of motion. Understanding these mechanisms provides insight into how the brain constructs our perception of movement from static images.
Phi phenomenon: The phi phenomenon is an optical illusion where a sequence of images or lights, when shown in rapid succession, creates the perception of motion. This effect occurs when our brain fills in the gaps between static images, leading us to perceive smooth motion rather than a series of discrete frames. It's fundamental to understanding how we perceive motion in various contexts, linking closely to apparent motion, motion detection, and motion integration.
Short-range apparent motion: Short-range apparent motion refers to the perception of movement that occurs over a brief distance and time interval, often observed when two or more stimuli are presented sequentially in close proximity. This phenomenon is a fundamental aspect of how we perceive motion, as it relies on the brain's ability to interpolate between static images, creating the illusion of smooth motion. It plays a crucial role in understanding how we interpret visual sequences and the mechanisms involved in motion perception.
Spatial frequency: Spatial frequency refers to the level of detail present in a visual stimulus, measured by the number of cycles of a repeating pattern per unit of visual angle. It is important for understanding how the human visual system processes images, particularly in distinguishing features like edges and textures. Different spatial frequencies correspond to different aspects of visual information, influencing our perception of motion and depth.
Stimulus onset asynchrony (soa): Stimulus onset asynchrony (soa) refers to the time interval between the onset of one stimulus and the onset of another stimulus in a sequence. This concept is crucial in understanding how different stimuli interact with each other in the perception process, particularly when examining phenomena such as motion perception and attentional processes. The manipulation of soa can influence how quickly or accurately individuals perceive motion or detect subsequent stimuli.
Stroboscopic motion: Stroboscopic motion refers to the visual illusion of movement that occurs when a series of still images is presented in rapid succession, creating the perception of fluid motion. This phenomenon is closely related to how we perceive apparent motion and how our visual system integrates discrete motion signals into a coherent whole.
Temporal frequency: Temporal frequency refers to the rate at which visual stimuli change over time, typically measured in hertz (Hz). It is crucial for understanding how we perceive motion, especially in cases where images or scenes appear to shift rapidly, creating an illusion of movement. This concept is essential for grasping how our visual system processes sequences of images or flashes to create a continuous experience of motion.
Ternus-pikler display: The ternus-pikler display is a perceptual phenomenon used to understand apparent motion, where two or more stimuli are presented in a specific sequence, creating the illusion of motion between them. This display helps researchers study how the human visual system perceives movement and the temporal and spatial factors influencing this perception. It is often utilized in experiments examining how motion is perceived even when there is a lack of actual movement in the stimuli.
Transformational apparent motion: Transformational apparent motion refers to the visual phenomenon where two or more static images are perceived as a continuous movement due to their sequential presentation. This type of motion involves a change in shape or form between the images, allowing the brain to interpret these transformations as dynamic motion, creating a seamless perception of movement.
Waterfall illusion: The waterfall illusion is a visual phenomenon where, after staring at a moving stimulus, such as a waterfall, for an extended period and then looking away, stationary objects appear to move in the opposite direction. This effect highlights how our perception of motion can be influenced by adaptation to movement in the visual field, revealing important aspects of apparent motion.