Image Stimuli

Version: v1 (current)

Display a single image to participants for perceptual, affective, or memory studies.

Overview

The Image stimuli task allows controlled presentation of scenes, faces, or objects. It supports both uploaded images and external URLs, with configurable dimensions and timing.

Common research uses include:

Face recognition: Show a face during encoding for later recognition testing
Scene memory: Present photographs for later recall
Visual priming: Brief image exposure before a target task
Stimulus rating: Show an image for subjective evaluation (paired with a questionnaire)

Where to Configure

Study form → Tasks → Stimuli tasks → Image → Configure.

Configuration Parameters

Image-Specific Parameters

Parameter	Type	Default	Description
Media URL	string	''	URL or uploaded image path
Image Width (px)	number	400	Display width of the image
Image Height (px)	number	400	Display height of the image
Maintain Aspect Ratio	boolean	true	Preserve the image's original proportions

Common Stimuli Parameters

Parameter	Type	Default	Description
Display Duration (ms)	number	0	Duration to show stimulus (0 = until participant advances)
Auto Advance	boolean	false	Auto-advance after duration (requires Display Duration > 0)
Button Text	string	'Continue'	Text for advancement button
Show Timer	boolean	false	Display countdown timer
Background Color (hex)	string	'FFFFFF'	Background color

Participant Flow

The participant sees the image displayed on screen.
If self-paced, the participant views and clicks the button to continue.
If timed, the image is shown for the specified duration and may auto-advance.

Design Recommendations

Resolution: Use high-quality images (at least 800x600); ensure consistent aspect ratios across stimuli.
Encoding studies: Use fixed durations (e.g., 2 s per image) for consistency.
Subliminal priming: Very brief exposure (17-33 ms), followed by a mask image.
Licensing: Use properly licensed images; document sources and categories.
Normed sets: Use validated stimuli with published norms (e.g., IAPS images, NimStim faces).

Common Issues and Solutions

Issue	Solution
Image doesn't load	Use absolute URLs; check CORS settings; test on the target browser
Image distorted	Enable Maintain Aspect Ratio; specify both width and height consistently
Participants skip too quickly	Use Auto Advance with a fixed Display Duration; disable the button until time elapses

Data Output

Markers and Responses

Markers (stimulus_shown):

{
  "type": "stimulus_shown",
  "ts": "2024-01-01T00:00:01.000Z",
  "hr": 1234.56,
  "data": {
    "type": "image",
    "url": "https://example.com/images/face01.jpg"
  }
}

Markers (response_recorded):

{
  "type": "response_recorded",
  "ts": "2024-01-01T00:00:05.000Z",
  "hr": 5234.56
}

Response Data:

{
  "type": "image"
}

Summary Artifact

None. The image stimulus task does not generate a summary artifact.

References

Bradley, M. M., & Lang, P. J. (2007). The International Affective Picture System (IAPS) in the study of emotion and attention. In J. A. Coan & J. J. B. Allen (Eds.), Handbook of Emotion Elicitation and Assessment (pp. 29-46). Oxford University Press.

Visual stimuli databases:

IAPS: International Affective Picture System (emotional images)
NimStim: Facial expressions database
BOSS: Bank of Standardized Stimuli (objects)
Faces Database: Chicago Face Database, Karolinska Directed Emotional Faces

Overview​

Where to Configure​

Configuration Parameters​

Image-Specific Parameters​

Common Stimuli Parameters​

Participant Flow​

Design Recommendations​

Common Issues and Solutions​

Data Output​

Markers and Responses​

Summary Artifact​

References​

See Also​