Application of Weber’s Law on Visual Perception

[pic 1]

Experiment No. 2

Application of Weber’s Law on Visual Perception

Abstract

The aim of the study is to determine whether if Weber’s Law applies to judgement of sizes. To find out if it’s true the researcher conducted an experiment using various lines to be drawn by the subject. The subject was asked to pinpoint the middle of each line ranging from 2 inch to 6 inch, each sizes composes of 10 lines, arranged randomly. The results shows that as the length of each line increases, the more the subject commits an error. Weber’s Law states that the differential threshold or just-noticeable-difference (JND) is proportional to the physical intensity of the stimulus (Ross & Wade 2009).

Introduction

Ernst Heinrich Weber was an anatomist and physiologist in Leipzig whose research centered on cutaneous sensation. He conducted an investigation to determine whether

[pic 2]

active engagement of one’s muscle affected one’s judgement of the weighs of object. Weber discovered that judgements were more accurate when subjects actively engaged their muscles; but he noted something interesting in subject’s abilities to detect a difference between the standard and comparison weights (Kantowitz, Roediger III, & Elmes 2015). This notion leads to the value frequently called just noticeable difference. JND is defined as the minimum increase in stimulus energy needed to elicit the sensation of a different stimulus.

Weber also found out that for a particular sensory modality, the size of difference threshold relative to the standard stimulus is constant. After almost twenty years, while searching for a fundamental law that governed the translation of physical energy into its psychological or mental representation Gustav Fechner stumbled upon Weber’s discovery. He elaborated his work and established another threshold, the absolute threshold. The absolute threshold of a particular sense is the minimum amount of stimulus energy needed to elicit a sensation (Allen, 1981). The underlying factors influencing our decision-making that happened inside the brain were further studied.

A chain of neural reactions were used to form an idea between the link in perception

[pic 3]

and action. Thus, stimulus guided one’s behaviour to make a decision regarding a particular action or motor response. Theoretical models of decision-making with biologically realistic neural circuits involves two populations of excitatory neurons engaged in competitive interactions mediated by inhibition, and extra sensory inputs that bias this competition in favour of one of the populations, producing a binary choice that develops gradually. Deco and Rolls (2006) found out that statistical fluctuations and divisive inhibition in an attractor decision-making network can be related to Weber’s Law. This law was used in their experiment to investigate the probabilistic behaviour of the neural responses responsible for detecting a just-noticeable difference stimulus.

Another stimulus which is subjected to Weber’s Law is time perception. It is base on behavioural studies about adults, children, and nonhuman animals. It is found out that it is the ratio between two durations rather than their absolute difference that controls the ability of an animal to discriminate them. It’s because timing behaviour shows scalar variability. The scalar variability has been interpreted based on the increasing value of the variability in temporal representation in comparison to the mean of the interval being presented (Brannon, Libertus, Meck, & Woldorff, 2008).

The researcher was interested to investigate if Weber’s Law applies to visual stimulus.  Thus, the researcher analyzes the influence of Weber’s Law in visual perception.

[pic 4]

This was assessed by letting the subject to pinpoint what one’s think is the midpoint between lines with various lengths.

II. Method

Objective – To find if the Weber’s Law applies to judgement of size.

Apparatus:

Paper with 2-, 4-, and 6-inch lines beginning at different starting positions from the edge. There should be 10 lines of each length, arranged in random such that the same length does not appear successively. (Appendix B)

Procedure:

Each student is his or her own S. Use a sheet of paper to mask the lines so that only one line is seen at a time. S examines each line and marks lightly with a ball pen what appears to be the mid-point. When all 30 midpoints have been “subjectively” marked,

[pic 5][pic 6]

[pic 7][pic 8]

Discussion

The results shows that the S was able to estimate the actual mid-point of the line more in 2-inch length rather than in 4 inch and least in 6 inch.   It was observed that as the size of the length increases the amount of error committed by the S also increases. The outcome was somewhat parallel in Weber’s findings. It was illustrated in Weber’s illusion. It is stated that if two distinguishable compass points are moved over parts of the body, the distance between two points seems to shrink or grow in those areas where the two-point threshold is larger or smaller (Ross & Wade, 2010).