Fraser J (1908) A new visual illusion of direction. Straight horizontal lines may appear skewed (e.g., the café wall illusion, It is known that a single stimulus may yield very different shape interpretations.
An optical illusion named after British psychologist James Fraser, who first studied the illusion in 1908 (Fraser 1908). We studied neural correlates accompanying the Fraser spiral illusion. Supplementary The Fraser spiral illusion consists of twisted cords superimposed on a patchwork background arranged in concentric circles, which is typically perceived as a spiral. The Fraser spiral illusion is an optical illusion that was first described by the British psychologist Sir James Fraser (1863 – 1936) in 1908.. The illusion is also known as the false spiral, or by its original name, the twisted cord illusion.The overlapping black arc segments appear to form a spiral; however, the arcs are really a series of overlapping concentric circles. The illusion is also known as the false spiral, or by its original name, the twisted cord illusion. Event-related potentials peaking around 200 ms after stimulus onset have been related to the detection of basic features such as brightness, color, and motion (An additional effect in the early time window (220–280 ms) is that amplitudes are highest for both illusory displays, although this was significantly different only for the circle stimulus/spiral percept.
Signals were filtered with a band-pass of 0.01–100 Hz and a notch filter to remove 50 Hz interference. All interelectrode impedances were kept below 5 kΩ. The experiment consisted of four blocks, and every block consisted of 75 trials (15 trials per condition including the control-stimuli, randomized). Eye blinks were monitored with electrodes placed below and above the eye. The spiral shape is not as prevalent as the circle in our natural environment. The illusion is also known as the false spiral, or by its original name, the twisted cord illusion.The overlapping black arc segments appear to form a spiral; however, the arcs are a series of concentric circles. This study was approved by the local ethics committee of SWU.The experiment included four kinds of stimuli: the original Fraser spiral illusion in which a set of concentric circles is made up of twisted cords (referred to as Twisted Circles, see Figure In the actual experiment, the task was to make shape judgments to each display.
Although the data do not contradict the view that the differential effects on the Fraser illusion already kick-in in the early time window, a general conclusion with regard to an EEG-signature linked to the percept or illusory appearance would require further testing with different sets of stimuli, also controlling for stimulus complexity and/or familiarity. The overlapping black arc segments appear to form a spiral; however, the arcs are a series of concentric circles. |
Cords."
The The history of this article since it was imported to Note: Some restrictions may apply to use of individual images which are separately licensed. The Fraser spiral illusion is an optical illusion that was first described by the British psychologist James Fraser in 1908.. The experiment lasted for approximately 15 min.Brain electrical activity was recorded with a sampling rate of 500 Hz using 64 electrodes which were mounted in an elastic cap (Brain Products GmbH, Munich, Germany) and located at the standard positions of the surface of the scalp (International 10/20 system). View all
The overlapping dark arc segments appear to form a spiral; however, the arcs are a series of concentric circles.The visual distortion is produced by combining a regular line pattern (the circles) with misaligned parts (the differently colored strands). In reality, the arcs that make up the "spiral" are actually a series of concentric circles. The Fraser spiral illusion is an optical illusion that was first described by the British psychologist Sir James Fraser (1863 – 1936) in 1908. The parallel circle stimulus was mainly seen as a set of circles, whereas the parallel spiral turned out to be rather ambiguous. The spiral form ofthe illusion has been the subject of the only other extensive study ofthe Fraserillusion since Fraser'soriginal report (Cowan, 1973). The alleged Percept effect in the later time window anterior area at first sight seems to be in agreement with other studies relating late positive waves to perceptual processing. Notice that this interaction effect can also be driven by a veridical vs. illusion distinction, with illusory percepts (circle stimulus/spiral percept; spiral stimulus/circle percept) resulting in different values from veridical percepts (circle stimulus/circle percept; spiral stimulus/spiral percept). This is the Fraser spiral illusion. The overlapping dark arc segments appear to form a spiral…