Chapter 1. Lexical Decision

1.1 Introduction

When you see a sequence of letters, you must figure out whether that sequence is a word (which, in effect, means "a word you know") or just random letters. Consider the letter sequences HELLO and HOLEL. The former is a word; the latter is not. Discriminating between words and non-words is called a lexical decision. In this experiment you will be asked to make lexical decisions about strings of letters.

1.2 Experiment Setup

1.3 Instructions

You will need to press the space bar to begin the experiment. A fixation mark will then appear in the center of the screen. Please look at this mark. After a brief period, it will be replaced by the prime stimulus, either a word or a string of letters that does not make up a word. There will then be another blank interval, followed by the target stimulus, which will be either a word or not a word. Your task is to indicate, as quickly and accurately as possible, if the second set of letters is a word or not a word.

Keyboard Responses

1.4 Experiment

1.5 Results

1.6 Debriefing

Two letter strings were presented on each trial, but you only had to respond to the second string. Still, in most experiments, what the first string is seems to influence how fast you respond to the second string. Let us first consider the trials where the two strings are both words. If the prime word has a meaning that is similar to the target word, then usually you will respond more quickly than if the two words are less closely related or are unrelated. Several interesting conclusions can be made from this observation. First, you seem to read words presented right in front of you whether you want to or not. Otherwise, why would words you don’t have to respond to alter the reaction time? That finding seems to support the automaticity of reading that was discussed as part of the Stroop experiment, which is also part of Cognitive Toolkit. Second, it seems reasonable, and many researchers have concluded, that when you access one word in memory by reading it, you also access, to a lesser degree, words that have similar meaning. Thus, prime-presenting the word "bird" will cause you to access related words to some degree. Then if the word "robin" is target-presented, it is already partly active and allows you to respond to it more quickly. It is almost as if accessing a word by reading it makes the memory representation become active and some of this activity spreads to words that are connected to it in some way. This idea that activity spreads, a spreading activation model of memory, is only possible if memories are stored in such a way that they are connected. The stronger the connection – such as having more similar meanings – the more the activation can spread.

References:

Ratcliff, R., Gomez, P., & McKoon, G. (2004). A diffusion model account of the lexical decision task. Psychological Review, 111, 159-182.

1.7 Quiz