The Effects of Optical Illusions in Perception and Action in Peripersonal and Extrapersonal Space

Exploring perceptual grouping by proximity principle in multistable dot lattices: Dissociation between vision-for-perception and vision-for-action

Perceptual grouping, a fundamental mechanism in our visual system, significantly influences our interpretation of and interaction with the surrounding world. This study explores the impact of the proximity principle from the perspective of the Two Visual Systems (TVS) model. The TVS model argues that the visual system comprises two distinct streams: the ventral stream, which forms the neural basis for "vision-for-perception," and the dorsal stream, which underlies "vision-for-action." We designed a perceptual grouping task using dot lattices as well as a line-orientation discrimination task. Data were collected using vocal and mouse methods for the vision-for-perception mode, and joystick and pen-paper methods for the vision-for-action mode. Each method, except for vocal, included separate blocks for right and left hands. The proximity data were fitted using exponential and power models. Linear mixed-effects models were used for the statistical analyses. The results revealed similar line-orientation discrimination accuracy across all conditions. The exponential model emerged as the best fit, demonstrating adherence to the Pure Distance Law in both perceptual modes. Sensitivity to the proximity principle was higher in the vision-for-action mode compared to the vision-for-perception. In terms of orientation biases, a strong preference for vertical orientation was observed in the vision-for-perception mode, whereas a noticeable preference toward either of the oblique orientations was detected in the vision-for-action mode. Analysis of free-drawn lines demonstrated an affordance bias in the vision-for-action mode. This suggests a remarkable tendency to perceive organizations within specific orientations that offer more affordances due to the interaction between the body postures and tools.

The effects of Müller-Lyer illusion on toe clearance height in stair ascent

BACKGROUND

The appearance of a stair can impact the safe negotiation of stair climbing. Increasing toe clearance height is a common strategy for reducing the risk of tripping when stepping onto a raised surface.

RESEARCH QUESTION

Can the Müller-Lyer illusion cause people to increase their toe clearance height when walking over a stair?

METHODS

Indoors, 15 healthy individuals (9 women and 6 men) walked up a 3-step staircase with each step 60 cm wide, 18 cm tall, and 30.5 cm deep. Outdoors, 253 people walked up a 2-step staircase with each step 6 m wide, 15 cm tall, and 38 cm deep. Four visual conditions were displayed at both the indoor and outdoor locations: fins out, fins in, line, and control.

RESULTS

While the fins out stairs were perceived taller than all the other displayed stair conditions, the toe clearance height was not different between display conditions when tested indoors. However, toe clearance height was greater in the fins out condition when compared to all other conditions for the outdoor stairs location.

SIGNIFICANCE

In the natural environment when walkers were oblivious to themselves being filmed and not having any knowledge of the task demand, the Müller-Lyer illusion significantly impacted their toe clearance height.

Directional aiming bias in golf putting

Johnston, Benton, and Nishida (2003, Last but not least - Golfers may have to overcome a persistent visuospatial illusion. Perception, 32(9), 1151-1154) reported that when standing sideways to hit a golf ball, it becomes very difficult to see the veridical line of putt to the target and it creates a bias to misread the direction to the right of target. The purpose of the study was to determine if this perceptual aiming bias also impacts putting. A group of expert (N = 24) and novice (N = 24) players performed a perception task of aligning a line on the golf ball towards the target hole and an action task of putting a ball to the target hole located 1 m and 4 m away. Novice players showed large perceptual aiming bias and small action aiming bias of putting. Yet, expert players showed neither bias in perceptual aiming nor in putting. This replicates earlier work (van Lier, van der Kamp, & Savelsbergh, 2011 Perception action in golf putting: Skill differences reflect calibration. Journal of Sport & Exercise Psychology, 33(3), 349-369) and was explained by the two-visual-pathway hypothesis. Despite the results showing some favorable support for the two-visual-pathway hypothesis, possible limitations are discussed.