Skip to main content

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. You upload a single image, optionally add rich-text instructions, and the participant advances by clicking the continue button.

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​

ParameterFieldTypeDefaultDescription
Imagestimuli_media_urlstring''The uploaded image. Use the Upload image button to choose a file; a preview and the file name are shown once uploaded.
Main Instructionsmain_instructionsstring (HTML)''Rich-text instructions shown on the dedicated instruction page before the stimulus.

The image is uploaded through a file picker (accept="image/*"); there is no plain-URL input field. The displayed image is rendered at its natural aspect ratio, scaled to fit the viewport (object-contain, up to max-h-[60vh]). There are no width/height, display-duration, auto-advance, timer, or background-color parameters for this task.

Participant Flow​

  1. The participant sees the image displayed on screen.
  2. The participant views the image and clicks the continue button to advance. The task is self-paced; there is no timed or auto-advance mode.

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​

IssueSolution
Image doesn't loadRe-upload the image; verify the upload completed and a preview appears in the config
Image looks too small or too largeThe image is scaled to fit the viewport at its natural aspect ratio; prepare source images at a suitable resolution before upload

Data Output​

Markers and Responses​

Marker (stimulus_shown) — emitted when the image is first shown:

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

Marker (stimulus_aoi) — emitted after paint, recording the image's on-screen bounding box (viewport-percentage units, top-left origin) so gaze samples can be joined to the stimulus area. Recording is best-effort and may be absent:

{
  "type": "stimulus_aoi",
  "ts": "2024-01-01T00:00:01.050Z",
  "hr": 1284.56,
  "data": {
    "stimulus_bounds": {
      "x_pct": 30.0,
      "y_pct": 12.5,
      "width_pct": 40.0,
      "height_pct": 60.0
    }
  }
}

Response Data — recorded once when the participant clicks continue:

{
  "type": "image",
  "stimulus_url": "https://example.com/images/face01.jpg",
  "viewing_time_ms": 4200,
  "responded": true
}

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

See Also​