Visual Search

 

INTRODUCTION

You are meeting a friend in the main concourse of Grand Central Terminal in New York City, in which thousands of tourists and people getting on and off trains pass through every day. Because of the hordes of people, you worry about being able to find your friend. However, he has promised to wear a bright red coat so he will be easier to spot.

Psychologist Donald Broadbent developed filter theory in 1958 to explain the selective nature of our attention, or conscious awareness. Your friend’s plan cleverly takes advantage of our selective attention abilities. Your brain is continually bombarded with visual and other sensory information than it can be conscious of at once. Your mind copes by automatically screening, or filtering, incoming sensory information to let in only what is most important.

In the main concourse of Grand Central, your friend’s red coat will serve as a salient feature that your mind can use to selectively ignore surrounding distractors (in this case, the hundreds of other people in the concourse). If you correctly apply your selective attention filter, you should be able to ignore all of the inputs you’re trying to block (anyone not wearing red) and focus specifically on your target: the red coat.

Your friend’s plan was perfect, right? But what if he arrives at the exact time as a throng of visiting St. Louis Cardinals fans (all wearing Cardinals red, of course) who are passing through the concourse on their way to Yankee Stadium, in which the Cardinals will be playing the New York Yankees?

The red-clad Cardinals fans will make your search a lot more difficult, since their red jerseys will become distractors. They might make it through your brain’s selective filter and become stimuli that your mind attends to (focuses attention on) even though they are not your target (your friend).

Selective attention filters enable us to make more automatic decisions about the stimuli around us, including which items to pay attention to during a visual search. In this ZAPS lab, you will participate in a classic psychological experiment that uses visual search tasks to explore fundamental processes of visual perception and attention. These tasks (also called feature search tasks) stem from research on attention by psychologist Anne Treisman. Exploring them should help you understand one of the ways our attention to specific features functions.

Instructions

As you learned in the Introduction, an object of interest is more or less salient in a field of other objects. This depends on prominent visual features including color, shape, size, and movement. The purpose of this ZAPS lab is to see how such features, in addition to the number of objects in the visual field (called distractors), influence how quickly we can find a target object.

Your task is to decide, as quickly as possible, whether a particular target object—in this case, a blue circle—is present in an array of other shapes. If the blue circle is present, click “yes.” If the blue circle is not present, click “no.” For example, you would click “yes” if the following array was presented because a blue circle is present.

In this experiment, you need to quickly decide whether your target, a(n) _________, is present in each array of objects.

Click or tap a choice to answer the question.

orange square

orange circle

blue circle

blue square

Correct!

This answer is correct.

You answered the question correctly on your first attempt, so your grade for the question is 100%.

 

Experience

 

 

 

 

Data Introduction

You completed the various trials in three different conditions, measuring three independent variables. The first being that sometimes the blue circle was present, other times it was not. The second independent variable was that sometimes only 4 objects appeared in the array, other times 16, and then as much as 64. The third independent variable was the nature of the distractor objects.

The first set of trials asked you to find the blue circle amidst orange squares and orange circles. This is an example of a feature search task because you were able to search for a single feature (“blueness”) that distinguished the target from all the distractors.

In contrast, the second set of trials asked you to find the blue circle amidst blue squares and orange circles. This is an example of a conjunction search task because no one feature distinguished the target from the distractors (some distractors were blue and some were circles) and you were forced to search for a conjunction of two features—color (blue) and shape (circle).

The key question is how much your reaction time—how quickly you decided whether or not the blue circle was present—was influenced by these three variables: 1) the presence or absence of the blue circle; 2) the complexity of the array; and 3) the type of search task. For a task that is relatively easy, we expect to see relatively quick reaction times.

On the graph that follows, you will see reaction time (in milliseconds) plotted along the y- axis, and the number of objects in each array (4, 16, or 64) plotted on the x- axis. Different lines will represent the presence or absence of the blue circle (“yes” and “no” trials) and the type of search task (Feature Search or Conjunction Search).

Based on your experience during the experiment, which combination of variables do you think resulted in the quickest reaction time? The slowest reaction time? Why?

 

You will initially receive full credit for any answer, but your instructor may review your response later.

 

YOUR DATA

· Graph

· Table

· Raw Data

 

 

 

DISCUSSION

According to Anne Treisman’s feature integration theory about attention and recognition, we begin a visual search by automatically indentifying “primitive” (or simple) features—such as color, shape, size, and movement—within an environment. She further proposed that our mind uses separate systems to analyze the different visual features of objects at the same time. This ability is called parallel processing. We can attend selectively to one feature by effectively blocking the further processing of the others (Treisman & Glade, 1980).

 

Sample trial from the  feature search  part of the Experience.

Sample trial from the  conjunction search  part of the Experience.

 

In the first set of trials—the feature search part of the Experience—you were asked to search for a single, simple feature, the color blue. Searching for a single stimulus, such as the blue circle (or your friend’s red coat in the Introduction), happens fast and automatically through what is known as pre-attentive processing. We do not need to deliberately focus to process this sensory information. The target was so salient that it seemed to “pop out” immediately, regardless of the number of distractors.

In the second set of trials—the conjunction search part of the Experience—your task was more complicated. You were asked to find the blue circle amidst blue squares and orange circles. It is a conjunction search because the stimulus you are looking for is made up of two simple features (color and shape) that are conjoined. When searching for two features, you need to look at the stimuli one at a time since your mind is not able to automatically process the tasks. Not only does it take longer, it also requires more attention. Because you had to deliberately focus, it is highly likely that your reaction times were higher for these trials.

Our ability to filter and selectively attend to sensory information doesn’t only affect our conscious awareness of visual information. Our auditory attention also allows us to listen selectively. In fact, the mind has many means of coping with the influx of information it receives—and most of the time, we are unaware they are occurring.

How might you be able to find your friend in the red coat at Grand Central Terminal even if he is amidst a huge crowd of other people wearing red?

 

You will initially receive full credit for any answer, but your instructor may review your response later.

 

LEARNING CHECK

Answer the following questions to complete this ZAPS activity. Your performance in this section accounts for 10% of your grade.

Imagine you have been asked to find the following object pictured on the left in the accompanying array on the right.

What type of search do you think this would be?

Click or tap a choice to answer the question.

conjunction search feature search

Imagine you have been asked to find the following object pictured on the left in the accompanying array on the right.

What type of search do you think this would be?

Click or tap a choice to answer the question.

feature search conjunction search

Based on the ideas presented in this ZAPS lab, which of the following tasks would you expect to be the most difficult visual search for someone to complete?

Click or tap a choice to answer the question.

finding two black socks in a laundry basket otherwise filled with white socks

finding the teacher in a preschool classroom amidst a group of 4-year-olds

finding the 3 of spades in a deck of 52 playing cards that vary by suit (hearts, diamonds, clubs, and spades) and number (aces, numbers 2-10, jacks, queens, kings)

finding the green M&Ms in a bag of M&Ms