Reaction Time for Detection of Object in Visual Search

 Reaction Time for Detection of Object in Visual Search

Abstract

The aim of this study is to investigate reaction time in visual search. 39 participants performed a reaction time test in different conditions, within different colours of letters and different number of letters. Based on previous research the hypothesis was supported, that there was significant difference in condition of number of letters. However, there was no significant difference found between one and five letters.

Introduction

Visual search is a process that requires attention and perception to detect particular object in environment. We use visual search in our everyday life such as when we go shopping and looking for certain items, when we are looking for our friends in a crowd.

Treisman et al (1977) introduced a feature integration theory of attention that suggested that in perception features come first. According to this proposed model, features are registered automatically and early, object are identified separately and later and focused attention necessary (Treisman et al, 1977, p. 98). Theory suggests that focused attention necessary to integrate different features together at the same visual location. When features are combined incorrectly illusory conjunctions occur (Treisman et al, 1980, p.98). According to Treisman (1980) there are two categories of visual search, a feature search and a conjunction search. Colour, orientation and intensity also required to perceive in visual search performance. Focused attention is necessary for the accurate combination of features when more than one object is displayed (Treisman et al, 1977, p. 195.).

Treisman and Gelade (1980) tested visual search for targets implied by one or more disjunctive features, what they found that it appears in parallel across the spatial display. When they tested visual search for conjunction target they found that it requires a serial scan through all items in display that suggests that attention must be focused on each item.

Laberge (1973) suggested that visual search is combined by constant mapping of target and all distractors displayed, a process of ‘’unitization’’. Shiffrin and Schneider (1977) called this process ‘’automatization’’.

According to Kahneman and Henik (1977), attention is hierarchical, first, the group is seeing as whole not the elements of it. They presented an experiment of selective attention of mixing blue and red letters in grouped displays or checkerboard arrangements. In attempts to recall red letters participants of the study showed advantage in group displays. Study suggested that spatial grouping is important in focusing attention.

Detection of target items in visual search does not necessary requires the serial allocation of spatial attention (Wolfe, 2013, p. 309) as it usually will ‘’pop-out’’ when there is one distinctive stimulus. This quick identification of a target is because of its salient features (Reeves, 2007). For example, it is easy to notice a red apple in a plate of green apples as we use pop out effect to identify quickly.  In contrast to targets that are defined by feature conjunctions, the speed to detect such a target is unaffected by distractors (Treisman et al, 1980).   

In visual search studies presented the task is very simple – to measure the time required for participants to allocate the target. Reaction time (RT) and the set size slope are measured. Discovering how quickly people find information leads to knowing how people perform visual search (Veksler, 2011).

Khasawneb et al (2003) investigated human visual search strategies by eye-tracking experiment. They suggested that the area searched to detect the target and the accuracy of the task showed no correlation. Newell et al (2004) investigated memory processes by using 3D objects suggested object based memory.

Neider & Zelinsky (2006) suggested that background of display affects reaction time versus set size slopes.

There are three main types of reaction experiments (Welford, 1980). When there is only one stimulus and only one response it is called simple reaction time experiment. Other type is called recognition reaction time type, when there are stimuli that needs to be responded and others are distractors. Third type is called choice reaction time experiment, when participant responds to stimuli by pressing a key or any other signal when stimuli appear. For example, when participants are asked to press a key on a keyboard when a target appears on a screen.

According to Donders (1868) simple reaction time is shorter than a recognition time but the longest is choice reaction time. The average for simple reaction time is 220msec when recognition reaction time is 384msec (Laming, 1968). A slower reaction time is due to more complex choice. Previous studies suggest that more letters in recognition a particular letter slows down the reaction time compare to recognition to fewer letters (Teichner et al, 1974; Luce, 1986). One letter in symbol recognition reaction time averages from 420msec, for 6 letters- 630msec, every item added to the set increases reaction time by average 40msec (Nickerson, 1972).

The most recent study conducted by University College London and University of Edinburgh made fascinating discovery in their research claiming that slow reaction time could be the cause of death. They conducted a longitudinal study from 1990s for 15 years. More than 5000 participated in the study, age 20-59.Reaction time of participants was measured by simply pressing a button when they saw an image on the screen. During the study, a total of 7.4 % of participants died. The study indicates that those with slow reaction time has a 25% chance of dying of any cause vs. those with average reaction time. No correlation between reaction time and death from cancer or respiratory problems were found. This study suggest that reaction time can predict survival and even how our central nervous system works.

As this study conducted by University College of London, provides such findings, that reaction time is important to be researched. It is fascinating to make such predictions claimed just by simple reaction tests. Even understanding the way reaction time differs can help us to understand surroundings better as we could use reaction time for efficiently only when we understand the requirements of reaction time efficiency. There is no doubt that we need to understand the ability of our motor skills and how it to be more efficient.

Previous research suggests that the more stimuli presented the more time is needed for reaction to recognise the target. The goal of this experiment was to measure reaction time in various conditions of stimuli. The hypothesis of this study is that the reaction time will increase when more stimuli presented compare to reaction time with fewer stimuli.

 

 

                                                              Method

The study used quasi experimental design method within the participants. Independent variables of the study were condition of the trial, 1) any blue letter; 2) brown or green letter O; 3) green letter N. IV- number of letters, distractors. IV- display size. Dependent variables were reaction time and accuracy.

Participants

Participants of the study were 39 first-year Psychology students of the National College of Ireland, both males and females. A convenience sampling method was used.

        Material

The experiment was performed on computers by using visual search experiment software ePrime.

       Procedure

The study took place in a computer lab class in the National College of Ireland. Participants were seated in front of computers and first given the manual and introduction of the software. They were asked to complete a visual search experiment on a computer where they had to identify 72 visual displays of different coloured letters that varied in a number of letters displayed. Participants were asked to press ‘’yes’’ on a keyboard if 1) any blue letter; 2) brown or green letter O; 3) green letter N, appeared. Data was submitted from all 39 participants to measure RT and accuracy of responses.

 

 

Results

Descriptive statistics analysis was performed using SPSS. The results were conducted from within participants trails of three different conditions. Analysis of different number (N-702) of items showed the effect of items to be significant in conditions of fifteen and thirty letters (See appendix1). Condition of one letter M- 785.48; Five letters M-787.51; Fifteen letters M-876.85; Thirty letters M-1044.62.

This suggests that RT increased significantly when more items were displayed. RT increased most when thirty letters appeared (See appendix1).

Condition of colour (N- 936), suggest lowest RT in condition – Blue letter (M -783.24; SD-633.966) and condition – Green/Brown letter O (M- 791.97; SD- 423.597). Condition of Green letter N,shows significant increase in RT (M-1045.72; SD-563.489). Appendix2.

Accuracy also tends to be significantly similar in colour conditions (Appendix2). Lowest in Green letter N (M-.86; SD-.345) and presence of thirty letters (M-.87; SD-.331).

All results of the study leads to predicted hypothesis that there will be significant difference in number of letters condition.

Discussion

Results of the study (Appendix5 .) suggest that RT significant increase as more stimulus is added. This supports hypothesis and provides results that supports finding of previous research. It also suggests that one letter present is significantly similar to five letter condition Found by Martin et al research (1993) that RT is longer if only one stimulus is displayed than if two or more. As the results show (Appendix1.) one letter condition M-785.48; five letters M-787.51. RT is similar in both one letter and five letter conditions. That suggests that it takes the same time to respond to up to five displayed stimulus.

The main findings of this research are that RT increases as more stimuli presented however, RT shows no significant increase in one vs. five stimuli presented. It takes the same RT to recognize the target in display when one or five letters presented.

In general, true/laboratory experiments are high in ecological validity as it is much easier to manipulate variables; there are still limitations and treats to be considered.

The experiment was performed at the computer laboratory class in college, which lacks of true ecological validity. A low number of participants (39) also lacks of meaningful results from such a small sample.

Use of certain substances prior to the experiment could also affect performance on experiment. Santos et al (2014) conducted a study of caffeine's effect on simulation of taekwondo performance. They found that caffeine reduced reaction time in performance. That leads to suggestions that experiment could be affected because of such as external factors like caffeine intake.

As there were several trails performed, a practise effect could occur, especially for psychology students. Experiment could have been affected by novelty affect, as participants possibly express more enthusiasm and focus on the task than outside the laboratory.

Such factors like age could also affect reaction time. Reaction time and time in recognising the stimuli in older adults is usually slower (Macdonald et al., 2008). The age of participants should also be considered prior reaction time experiments. Noble et al (1964) found that males have faster reaction time than females, however, more recent studies suggest that there is no significant difference between males and females in reaction time (Jevas & Yan, 2001). It is also suggested that reaction time will be faster when identical stimuli follow compare to a mix of different stimuli (Sanders, 1998).

Many more aspects could possibly affect reaction time, some are known and some are still undiscovered. Even know the hypothesis of this research was supported, there is a lot that should be noticed, as age, gender, and even drinking coffee possibly affecting reaction time. That could affect us in everyday life, such as when driving or playing football. A recent study even suggests that we can predict death by a simple reaction time test. This study is open for new researches that should be considered with larger sample and even support for gender and age differences.