Lecture 16: Proprioception

Proprioceptive sensory neurons

• all over your body

• allows us to know the position of our body, keep balance, and sense muscle tightness

Damage to the proprioceptive system

Only 9 cases in the world! Can't control your arms - while looking to the right side, his left arm just starts flanking around and can hit people

Conflict of visual-proprioceptive cues

Disappearing hand trick

• A person putting their hand under a screen. Under the screen there are two cameras, and the person's task is to keep their hands between moving lines. However, one of the cameras slowly move to the right. Even as the participant moves their hand with the camera, it looks like their hand doesn't move at all, even though it's a lot further apart than it feels

Two crossed fingers demo

Stimulating the ‘outside’ parts of your middle and index fingers usually only happens when there are two objects

• The unusual positions of your fingers confuses your proprioceptive system

Vestibular system

sense of orientation

• exists in the inner ear, using 3 semi-circular canals with fluids that indicate rotational movements

• otoliths are in charge of our sense of gravity

Sense of orientation is affected by

verstibular, proprioceptive, and visual cues

• sense of pressure - you feel the ground you stand on and the direction your hair is falling

Irvin Rock (1956) ambigious figures study

showed that tilting our head doesn’t change our perception on orientation of images, need to actually rotate the image to see the actual figure

Orientation in face perception

Upright faces are processed better than inverted ones, using the retinal frame of reference

Egocentric

Retinal, head, body

• if you see an upside down face and you’re also upside down, it will look normal, thus aligning with your ego view

Allocentric

Enviornemntal, gravitational

Design to test different reference frames

Rotating the observer and having faces in different orientations (some that align with ego and some with env)

• best results when EGO up → env up → env down (not the worst since in life we always use env cues) → ego down

Exp 1: classifying emotional expressions of mooney faces

rotate right/left and classify orienated expressions

• Both EGO (large effect) and ENV (small effect) influence facial expression identification

Mooney faces

two toned faces

• difficult to recognize since they have shadows, which is used in real life to find orientations

Clock study

Reading clocks is influenced by both EGO and ENV angles

• Best reaction times when the clock was mostly aligned to you, but a little bit more upright

Reading study methods

Orientation on reading

Created a bunch of words and non-words to see RT and accuracy of reading based on orientation -- see a word and say if it's a real word or non-word

Reading study results

• Person is upright: Symmetric effect of orientation (+- 90) which is unexpected since we read from top to bottom

• Person is turned: A big asymmetry now: -90 takes a lot more time than 90. This is because 90 aligns with gravity

Reading study conclusions

• We have more experience reading words upright (aligns with the environment) even when our head is turned

• Both the orientation of the words relative to orientation and relative to the environment matter

How do people choose to orient a display screen when their body and head are in non-upright positions?

2 conditions: one with a room as the background and one with a black bg

VR Study conclusions

• No VE: preferred screen orientation increased as body rotation increased (halfway between ego and env 0)

• World-aligned VE (only screen rotated with the world) = wanted screen to be ENV-aligned

• EGO-aligned VE (screen and bg rotated w/ your body) = EGO-aligned

• upright body, tilted screen - no correlation

Participant analysis

lots of variety across participants, but each subject was consistent within themselves

• the best solution may be to display the screen without a virtual environment and

  give users the ability to manipulate the screen’s orientation