C6 - Chapitre Flashcards
What is the rotating snakes illusion an example of?
An optical illusion where a still image elicits the perception of movement.
What would Gestalt psychologists say about motion illusions like the rotating snakes?
That what we see is different from the sum of its individual parts.
What visual stream is involved in motion perception?
The dorsal visual stream.
What type of event is motion considered as?
A spatiotemporal event involving relative change of position in space over time.
Why is motion perception important for figure-ground segmentation?
Because moving objects are easier to distinguish from the background, like spotting a camouflaged animal when it moves.
How does motion perception help in social communication?
By allowing us to rely on movements of facial muscles and lips to interpret expressions and language.
Why is motion perception important for avoiding harm?
It helps estimate the trajectory of incoming objects to interact with or avoid them.
Why can’t the visual system rely on absolute distance and speed of approach to perceive motion?
Because we are not very good at estimating absolute values.
What cue does the visual system rely on for perceiving motion of approaching objects?
The increase in size of the retinal image as the object approaches.
Why is illumination not a reliable signal for motion direction?
Because it’s too noisy and easily disrupted by things like passing clouds.
What is required for the visual system to perceive motion between two flickering dots?
The dots must flicker within a specific speed range; too slow or too fast prevents motion perception.
How does distance between flickering dots affect motion perception?
Greater distances can disrupt the motion illusion if speed appears unrealistically fast for that span.
Why don’t we perceive motion when flickering is too slow?
The temporal sampling by the brain isn’t enough to interpolate smooth motion at low flicker speeds.
Why would a purely temporal sampling approach to motion perception be insufficient?
It would create a stroboscopic displacement effect instead of a smooth motion percept.
What simple model explains the detection of motion by adjacent neurons?
Neurons A and B with adjacent receptive fields activate a higher-level neuron M when an object moves across both fields.
What is the limitation of a basic motion detection model using neurons A and B feeding into neuron M?
It cannot distinguish movement direction, and static stimuli in both receptive fields also activate neuron M.
How can motion directionality be encoded in a neural circuit?
By adding an interneuron (D) that delays the input to one of the pathways, introducing asymmetry.
What is the function of interneuron D in the Reichardt detector model?
It introduces a delay that allows neuron M to become selective for a specific direction of motion.
What does the Reichardt detector model explain beyond direction selectivity?
It provides a mechanism for encoding direction and speed selectivity.
How can the Reichardt detector model encode speed selectivity?
By varying the delay from interneuron D, detectors can be tuned to respond to different speeds.
Where are Reichardt detectors likely first found in primates?
In the primary visual cortex, not in the retina as seen in some rodents.
What evidence supports the existence of Reichardt detectors in the primary visual cortex?
Hubel and Wiesel’s recordings of motion-sensitive neurons and the motion aftereffect demonstrate this.
What does the interocular transfer of the motion aftereffect suggest?
That motion-sensitive neurons are located in the cortex, since the adaptation transfers between eyes.
How can you experience the motion aftereffect with interocular transfer?
Close one eye and focus on the center of a motion video, then switch eyes after the video stops and observe a stationary object like your hand.
Why are Reichardt detectors not sufficient for global motion perception?
Because their receptive fields are limited and do not provide enough spatial information to detect full stimulus direction.
What is the aperture problem?
It is the spatial constraint where a motion-sensitive neuron detects motion in only one direction within its limited receptive field, missing the full motion.
What is apparent motion?
The illusion of movement caused by flickering stimuli at optimal speed, indistinguishable from real motion.
What optical illusion demonstrates the effects of apparent motion?
The wagon wheel effect, where rotating wheels appear to spin backward under certain conditions.
What is the correspondence problem in motion perception?
It refers to the difficulty in correctly matching stimulus features across visual frames, which can lead to illusions such as the wagon wheel effect.
What factors help the visual system solve the correspondence problem?
Proximity, similarities in color, orientation, and spatial frequency aid in matching features into a coherent motion path.
Which phenomenon illustrates the consequence of incorrect feature matching in motion perception?
The wagon wheel effect.
What area of the brain is involved in solving the correspondence problem in motion perception?
The middle temporal visual area (MT or V5).
How does binocular vision relate to the correspondence problem?
It faces a similar issue where inputs from both eyes must be coherently matched, a task handled by disparity-tuned neurons in V1.
What is the role of area MT in motion perception?
MT integrates inputs from multiple V1 local motion detectors to compute the global motion direction of an object.
Why are multiple V1 neurons needed to determine an object’s global motion?
Because each V1 neuron has a limited receptive field and may detect motion compatible with multiple global directions; combining inputs resolves ambiguity.
How does area MT solve the aperture problem?
By integrating motion signals from multiple V1 neurons with different receptive fields to determine the global direction of an object’s motion.
Who discovered the firing patterns of area MT neurons related to global motion perception?
William Newsome and his colleagues.
What percentage of dots moving in the same direction is sufficient for trained monkeys to detect global motion?
As low as 3%.
What happened to monkeys’ performance in detecting global motion after MT lesions?
Their performance was severely impaired.
What condition results from bilateral damage to area MT?
Akinetopsia, the inability to perceive motion.
What eye movement helps stabilize images on the fovea during tracking?
Smooth pursuit.
Which brain area is involved in smooth pursuit and responds only to volitional eye movement?
Medial Superior Temporal (MST) area.
What did Stevens et al. discover when they paralyzed their eye muscles?
They experienced vertigo because the world appeared to move when trying to move their eyes.
What are saccades?
Jittery eye movements that occur when trying to track a stationary target or rapidly changing fixation.
What are microsaccades?
Very small, involuntary eye movements that prevent visual fading and enhance detail visibility.
What is saccadic suppression?
A reduction in visual input strength during saccades to prevent image blur.
What causes saccadic suppression?
An active neurological mechanism involving inhibition in MT and parietal structures.
What visual illusion becomes stronger during saccadic movements?
The rotating snakes illusion.
What study documented a correlation between saccade amplitude and illusion saliency?
Kitakoa et al.’s study.
