Lab Report

Abstract

In this experiment, we measured subjective awareness by estimating the magnitude of perceptual illusions. In the perceptual illusions, big and small dots can be perceived to be different in size when presented by a standard dot. Two identical dots can also be perceived to be of different sizes when they are surrounded by smaller or larger dots. This size contrast illusion is known as Ebbinghaus Illusion, and it has a strong perceptual effect. In the experiment, we measure the subjective awareness among individuals by estimating the magnitude of perceptual illusions. We argue that when perception is subjected to the influence of large and smaller dots displays, the dots surrounding the baseline dot are also influential. This hypothesis was tested among 154 subjects who were asked to identify the size of the black dots and the ‘standard’, ‘small’, and ‘large’ inducers from the illustrations. The results showed that the perceptual estimation of the size of the black dots was influenced by illusion. The discussion analyses the results on the basis of perceptual illusions and how it influences subjective awareness among participants. 

Introduction

The magnitude of perceptual illusions can be used to measure the subjective awareness as the stronger the perceptual illusion, the greater the impact of subjective awareness. Attributes of an object are processed differently according to the task that is involved (Maruya, Holcombe, & Nishisa, 2013). There has been an increasing number of studies that involve visual illusions whereby some attributes of an object, for example, size, length or orientation are altered according to how an object is placed. Visual illusions can be useful in revealing the distinct functional pathways of the human brain as perception depends on the context of an object (Pavani, Boscagli, Benvenuti, Rabuffetti, & Farne, 1999). 

In a visual experiment, the relationship between objects is vital for object recognition as the context provides the information that allows the objects attributes to remain constant across different viewing conditions. In a study by Bridgeman, Kirch and Sperling (1981), subjects were asked to manually point at a fixed target surrounded by a frame. As the frame was moved, the fixed target appeared to be moving in the opposite direction. Despite this strong illusion, subjects were still able to point out the actual location of the fixed target. 

In another study by Aglioti and colleagues (1995), three dimensional version of Ebbinghaus Illusion circles were presented, and subjects were required to identify whether the discs were the same or different and grasp the discs. When the target discs were equal in size, the subjects reported that the disc surrounded by smaller discs was larger than the disc surrounded by larger circles. When the disc surrounded by smaller circles was 2.5 times larger than the disc surrounded by larger circles, the subjects perceived the discs to be equal in size. 

In a more recent study by Burg and Cass (2014), subjects were presented with a display of white circular fixation point with black target disks surrounded by distractor disks. The subjects were then asked what target event appeared first. The results showed that the presence of distractor events impaired visual temporal order judgements among the participants. In another experiment, Burg and Cass (2014) manipulated the target-distractor target by changing the colours from black to red. The results showed that distractor events impaired perceptual illusion in the context of strong colour segmentation cues.

The results of these studies show that perception is influenced by illusions. In all the studies described above, the perceptual estimation of the attributes of the objects was clearly influenced by illusions. The use of distractions creates illusions and objects are perceived to be different from what they really are. The observed effect of illusion on perception could therefore depend on the visual configurations and distractions. This means that the visual system is influenced by illusions and the different levels of attention across visual displays (Theeuwes, & Van der Burg, 2007).

In the present study, we exposed subjective awareness and perception to the same illusion according to our hypothesis. The experiment aims at measuring the subjective awareness by estimating the magnitude of perceptual illusions. We argue that when perception is subjected to the influence of large and smaller dots displays, the dots surrounding the baseline dot are also influential. Accordingly, the study participants were presented with one standard or baseline dot, and different dots were presented as comparisons in a number of trials. A larger dots array was used to induce underestimation of the size of the standard dot, while smaller dots arrays were used to induce overestimation of the size of the standard dot. In each trial, participants were asked to identify the size of the comparison dots as ‘standard’, ‘larger’ or ‘smaller’.

Discussion

The results of this experiment demonstrate that the Ebbinghaus Illusion dots presented induced an illusion of the size of the standard and comparison dots when larger and smaller dots were presented. When the larger inducer was presented as the comparison, the subjects considered the inducer to be larger 56% of the time. When the smaller inducer was presented as the comparison, the subjects felt like the inducer was larger than the comparison 59% of the time. When the baseline inducer was presented accompanied by large inducers and the comparison inducers were either large or small inducers, the proportion of times that the comparison disk was considered to be larger was 50%. 

These results are in accord with previous research that shows that the Ebbinghaus Illusion is effective when similar dots are presented. The small dots array caused an overestimation of the standard dot size in the visual tasks that involved identifying the size of the dots. In addition, the larger dots caused an underestimation of the standard dot size. It important to note that the magnitude of the perceptual illusion observed when there was an array of smaller or larger inducers surrounding the standard dot. When the original Ebbinghaus Illusion circles were adopted, the annuli of circles altered the perception of the target object by 2.5 mm (Aglioti, DeSouza, & Goodale, 1995). This means that when the annulus of circles is presented alone, the perception illusion is smaller than the illusion obtained when the larger and smaller dots are used together with the standard dot.

According to the hypothesis in the experiment, the perception is influenced by illusions in terms of visual display. This means that subjects perceived the standard and comparison dots as the same or different depending on the way they were presented. Another thing to consider about the results is that the smaller and larger illusionary arrays of dots presented affected the perceived dot size in different ways. Even though the smaller and larger dots determined an illusion of the standard and comparison dots, the magnitude of the illusion created by smaller dots was higher than the illusion created by larger dots. The strength of an illusion varies according to the spatial arrangement of circles in Ebbinghaus Illusion (Jaeger & Grasso, 1993). Nevertheless, it is important to note that the different visual illusion influence perception in different ways.

This experiment demonstrates that the presence of visual distractions around the object of focus can significantly interfere with the perceptions among individuals. The unique spatial distribution of the black dots in this experiment and the extent of their effect on perception demonstrate that illusions really affect the subjective awareness of individuals. While some participants were able to correctly identify the size of the standard and comparison dots, some were not able to give the correct sizes at all. The smaller dot arrays had the most profound effect in the perception of the participants.

 

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