PsychoPy Tutorial 1 | Adaptive Staircase Procedure | Orientation Discrimination

Summary

This tutorial demonstrates how to implement an adaptive staircase procedure in PsychoPy for an orientation discrimination task. It explains the process of titrating the minimum intensity value of a stimulus to find the threshold orientation difference for accurate detection. The video guides through setting up a simple task with a fixation cross, grating parameters, and keyboard responses, then introduces the adaptive staircase loop with parameters like start value, step sizes, and termination criteria. It concludes with analyzing data to determine the threshold value, showcasing the procedure's effectiveness in adapting to participant performance.

Takeaways

• 😀 The tutorial is about implementing an Adaptive Staircase procedure in PsychoPy for tasks like orientation discrimination.
• 🔍 The goal is to find the minimum intensity value of a stimulus for detection, such as the smallest orientation difference that results in correct responses.
• 👁️ The task involves identifying the tilt direction of a grating patch, which can be tilted left or right, and is presented after a fixation cross.
• ⏱️ The fixation cross appears for 500 milliseconds at the start of each trial, serving as a focus point for participants.
• 📊 The grating's orientation is a variable parameter that is manipulated throughout the experiment to determine the threshold.
• 🗨️ Participants respond using the left and right arrow keys to indicate the perceived tilt direction of the grating.
• 🔄 The Adaptive Staircase procedure adjusts the stimulus intensity based on the participant's responses, increasing after incorrect responses and decreasing after correct ones.
• 📉 The procedure uses a series of parameters including start value, step sizes, and step types to control the intensity adjustments.
• 🔢 The tutorial explains how to code the 50/50 probability condition for the grating's tilt direction and the corresponding correct response.
• 📊 Data recording includes variables such as correct response, direction, and accuracy, which are essential for the Adaptive Staircase algorithm.
• 📉 The final data can be analyzed to determine the threshold value, often calculated as the average of intensity values during reversals.

Q & A

What is the purpose of an Adaptive Staircase procedure in a psychophysical experiment?

The purpose of an Adaptive Staircase procedure is to estimate the threshold of stimulus intensity for detection or discrimination, such as the minimum orientation difference required for a participant to accurately identify the tilt direction of a grating.

What is the task for the participant in the orientation discrimination experiment described in the script?

The task for the participant is to correctly identify the tilt of a grating patch, which can be tilted to the right or left, or in other words, clockwise or counterclockwise.

What does the fixation cross in the experiment signify and how long does it last?

The fixation cross is a visual cue displayed at the beginning of each trial to direct the participant's attention. It lasts for 500 milliseconds.

What parameters define a grating in the context of this experiment?

The parameters that define a grating include orientation, size, contrast, and spatial frequency. The orientation is the critical parameter that will be varied in the Adaptive Staircase procedure.

How is the orientation of the grating determined in the experiment?

The orientation of the grating is determined by a variable parameter that changes with each trial. It is set to either a left or right tilt with a 50/50 probability using a random number generator.

What is the significance of specifying the correct answer in the Adaptive Staircase procedure?

The correct answer is crucial because the Adaptive Staircase procedure uses it to adjust the stimulus intensity for the next trial based on whether the participant's response was correct or incorrect.

How does the staircase procedure adapt the stimulus intensity based on the participant's response?

If the participant's response is correct, the stimulus intensity (e.g., orientation difference) is reduced. If the response is incorrect, the intensity is increased, thus adapting to the participant's performance.

What does 'reversal' mean in the context of an Adaptive Staircase procedure?

A 'reversal' refers to a change in the direction of the stimulus intensity adjustment. For example, if the intensity was decreasing due to correct responses and then an incorrect response causes the intensity to increase, that increase represents a reversal.

How can the threshold value be determined from the data collected in an Adaptive Staircase procedure?

The threshold value can be estimated by taking the average of the intensity values at the points of reversal, as these points represent the boundary between correct and incorrect responses.

What are the 'step sizes' in an Adaptive Staircase procedure and how are they used?

Step sizes determine the amount by which the stimulus intensity increases or decreases after a mistake or a correct response. Multiple step sizes can be specified, starting with a larger step size and progressing to smaller ones as the experiment continues.

How does the script guide the setup of the Adaptive Staircase Loop in PsychoPy?

The script explains how to add a loop around the routine, change the loop type to 'staircase', and define parameters such as repetitions, start value, max and min values, and step sizes to configure the Adaptive Staircase procedure.