An understanding of Collicular Ping-Pong
This activity involves the patient sitting with their hands at shoulder height while they are repeatedly bombarded with ping-pong balls thrown directly at the bridge of the nose between the eyes. The patient has to repeatedly hit the balls away from their face. See videos.
When the ball suddenly expands its size on the retina, looming sensitive retinal ganglion cells, fire and send a collision alert through the superior colliculus in the optic tectum to the Defensive Blink Centre for inhibiting the Levator Palpbrae muscle of the superior eye lid and firing the orbicularis oculi muscles. It triggers a brain stem saccade to quickly shift the eye to be looking at the object and updates the hand-target map of the Dorsal Visual Stream and the Parietal Reach region.
Repeatedly batting ping-pong balls forces this ancient millisecond range warning system to operate over and over sharpening the threshold at which the brain recognises an oncoming threat.
Actually hitting the ball requires finding it with a saccade predicting its time to collision from the retinal expansion rate and generating a reach that peaks where the hand and ball intersect.
This means the cerebellum converts ‘visual time’ into ‘limb muscle timing’ creating an efferent copy of the movement which is updated after every near miss. The parietal-frontal dorsal stream transforms retinotopic ball position into shoulder level motor coordinates, while the basal ganglia loops gate the rapid ‘go’ signal so the strike launches in less than 200 ms.
Each successful swat slightly reduces the visual motor latency (Hebbian plasticity), improving overall Hand-eye coordination.
A looming object evokes not only a cortical response as described above but also subcortical reflexes involving a ‘blink and head withdrawal’ to protect the cornea, a vestibular ocular reflex adaption, so that the eyes stay locked on the target while the head is in movement and the axial muscles will stiffen the trunk in a startle postural reflex.
Practising this drill will link the reflexes with the voluntary arm strike, forging a smooth defensive symmetry rather than a fragmented flinch.
The superior colliculus projects to the periaqueductal grey area and the hypothalamus, briefly raising sympathetic tone, which would show as increased heart rate and pupil dilation and likely creates a quick adrenaline micro-surge from the adrenal medulla.
With regular low threat repetitions, the limbic system is taught to modulate this surge giving enough arousal for speed but not so much that fine motor accuracy degrades.
Clinically the value of this activity will be especially useful for vestibular and concussion rehabilitation as it restores eye–head coordination and confidence when stimuli approach the face. For sports performance enhancement the activity produces faster ‘looming’ detection. Which can lead to an earlier swing/defence timing in racket & ball sports.
Importantly this activity can assist with Anxiety and startle disorders as graduated exposure to near-face stimuli lowers hyper-startle via habituation. Falls prevention in older adults would be expected as it improves protective reach reactions and visuomotor processing speed.
This activity simultaneously exercises, primitive collision avoidance circuits and higher order visual motor planning.
It creates a sharper looming reflex involving the retina, superior colliculus, blink and startle reflexes.
It gives a faster more accurate hand strike in involving the parietal cerebella sensory motor loop.
It allows a better stress modulation as the autonomic fight/ flight set point is altered.
Repeated practice blends those elements into an efficient goal directed defensive movement.
A bit more on looming.
Looming sensitive responses, which are those triggered when an object rapidly approaches, are found at the retinal ganglion cell level with specific ganglion cells and upstream Amacrine cells contributing to this important survival function.
Retinal ganglion cells are the output neurons of the retina with certain sub types that are specifically sensitive to looming motion. The looming sensitive retinal ganglion cells respond to expanding dark objects.
Amarcrine interneurons determine the ganglion cell response, bilateral inhibition and temporal tuning.
There are primarily two types.
Wide Field Amarcrine cells provide motion signal integration across large retinal areas for distinguishing global expansion from simple edge motion.
The Starburst Amarcrine cells are direction selective for modulating motionpathways relegated to threat detection.
Bipolar cells, while not selective for ‘looming’, feed into retinal ganglion cells and help encode contrast and temporal dynamics necessary for motion detection.
Of note is that looming represents a time critical survival threat. Therefore it is no surprise that we have evolved looming ability to be processed at the retinal level giving it very fast reaction times of less than 100 ms and triggering pre-cortical reflexes such as defensive blinking, freezing or escape behaviour. It directly communicates with the superior colliculus bypassing conscious vision.
Looming reaction circuits produce the earliest neural alert system for eminent collision to enable reflective and conscious avoidance.
Video: Each successful swat slightly reduces the visual motor latency (Hebbian plasticity), improving overall Hand-eye coordination