Experiment Two

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back index	The Attentional Blink
	Experiment Two: The Attentional Blink

Method:

Introduction:

The purpose of this study will be to test the hypothesis that the attentional blink reflects a loss in sensory processing. The primary aim will be to evaluate the experimental design, and the custom-made software. This study will utilise a generic attentional blink procedure, and will follow the general design used by Raymond et al (1992). Through a rapid serial visual presentation subjects will be asked to identify a partially specified target letter T1 (target one) and then detect the presence or absence of a fully identified letter T2 (target two). Previous research (Raymond et al (1992) has indicated that whenT1 is fully identified T2 is poorly detected when presented within 270ms of T1. WhenT2 is presented immediately within 180ms of T1 and after an interval of 270ms there is an increased possibility of it being accurately detected. Therefore it is hypothesised that participants will significantly report fewer incidents of T2 when presented within a temporal period of between 180-270ms after T1.

Method:

Participants: Top of page

In this pilot study just six subjects (N=6) will be required. It is expected that volunteers will be drawn from undergraduate psychology students within the department. The small sample size is comparable to other attentional blink studies e.g. Raymond et al. (1992) and Raymond et al. (1995), and is representative of a general trend in RSVP studies. There has been no evidence of a gender or an age bias in RSVP trials, therefore gender and age will not be considered confounding factors. All subjects will be asked to sign an informed consent form (see appendix One). In addition subjects will be asked if they have normal or corrected to normal visual acuity or are deficient in colour vision. Subjects will also be made aware of the fast flickering nature of the stimuli, and its very small risk of triggering an epileptic seizure. Subjects will be asked to complete a small number of practice trials, before taking part in the full experimental procedure.

Apparatus: Top of page

The stimuli will be created on custom-made software written in Experimental Run-Time Systems (ERTS) programming language (see appendix??). The subjects will view a colour 15inch-computer monitor from approximately 35 centimetres (20 inches). The monitor is expected to have a refresh rate of 60 hertz. Subjects will initiate each trial by pressing the letter "N" on a computer keyboard. At the end of each trial subjects will be required to answer two questions, responses to which will be recorded by the computer.

Stimuli: Top of page

The stimuli will consist of a stream of fifteen letters, two target letters and thirteen distracter letters. Target one (T1) will be differentially marked from the other RSVP items. T1 will consist of the letters R, S or T, and will be displayed in white whereas T2 will be an X and displayed in black. Non-target items (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, U, V, W, Y, Z) and other characters will be presented in black, shown against a uniform grey background. Each letter will be displayed for 15 milliseconds with an inter-stimulus interval of 75 milliseconds. T1 will appear after serial position six, and T2 will be displayed in any position after T1. On half the 120 trials T1 will not be presented. This will be called the 'target absent' condition or 'control' condition. In the 'experimental' condition, T1 will be present and the stimulus stream will be 15 items in length. The computer will randomly select equal numbers of control and experimental conditions.

Design: Top of page

A repeated measures design was utilised, such that each participant took part in all conditions of the independent variable, namely: 'target present' trials (experimental condition) versus 'target absent' trials (control condition). Probe detection was the dependent variable.

Procedure: Top of page

Each participant will receive 60 'control' and 60 'experimental' trials. Each trial will consist of a series of rapidly presented letters shown in the same spatial position with a temporal delay of 90ms between the start of each presentation. Before the start of each experimental period the subjects will be asked to attend to the entire RSVP stream. Subjects will be made aware that T2 is always an X displayed in black, and T1, displayed in white, and can be one of three letter, R, T and S. The subjects will initiate a trial by pressing the letter N on the computer keyboard. Initially a fixation dot will appear in the centre of the computer screen. After 1000ms the stream will begin. At the end of each trial, the subjects will be asked two questions "Did you see the letter in white?" and "Did you see the letter X?" The subjects will make their responses to each question by pressing the appropriate letter on the computer keyboard. There will be no time limit for each experimental period; however, it is expected that no experimental session will last longer than twenty-five minutes.

Results: Top of page

The raw data will be subjected to a correlated t-test. Means scores will be compared between T1 absent and T1 present. It is expected that the results will indicate that subjects failed to accurately report T2 in the presence of T1.