Image Grid Stimuli

Version: v1 (current)

Display multiple images simultaneously in a configurable grid layout.

Overview

The Image Grid stimuli task presents multiple images at once in a structured grid arrangement. It supports comparison, preference, visual search, and memory encoding paradigms where participants need to see several items simultaneously.

Common research uses include:

Visual short-term memory: Show a grid of items, then test recall or change detection
Scene arrays: Present multiple objects or faces for comparison
Choice displays: Show options for selection tasks
Change detection: Display arrays during encoding phases

Where to Configure

Study form → Tasks → Stimuli tasks → Image grid → Configure. Also available identically in edit mode.

Configuration Parameters

Grid-Specific Parameters

Parameter	Type	Default	Description
Upload images	file upload	-	Upload the image files to include in the grid (multiple selection)
Columns	number	3	Number of columns in the grid (clamped to 1-12)
Rows	number	2	Number of rows (minimum 1; auto-increases if images exceed Columns x Rows)
Fit mode	select	fit_screen	`fit_screen` (fit to screen, no scroll) or `original_size` (natural sizes, may scroll)

Instructions

Parameter	Type	Default	Description
Main instructions	rich text (HTML)	''	Instructions shown with the grid
Hint instructions	rich text (HTML)	''	Optional hint text

Grid Auto-Sizing

If the number of uploaded images (N) exceeds Columns x Rows, the editor automatically increases Rows to the minimum needed: R' = ceil(N / Columns). Columns remain fixed. Empty cells are displayed if Columns x R' > N.

Grid Arrangement

Reorder: Drag and drop any cell (image or empty) onto another cell to swap their contents. Empty cells behave the same as image cells for swapping.
Remove: Click the x in the top-right of any image cell to remove that image (the cell becomes empty). Remaining images keep their positions unless you explicitly swap them.

Participant Flow

The participant sees the configured grid with the saved arrangement (empty slots appear blank).
If paired with a response task, the participant responds.
The participant clicks the continue button to advance.

Example

Inputs: Columns = 3, Rows = 2 (C x R = 6).
Uploaded images: N = 8.
The editor computes R' = ceil(8/3) = 3, so the matrix is 3x3 (9 cells). Images 1-8 are placed in the first 8 cells (row-major order). The 9th cell is empty and draggable. Swapping Image 5 with the empty cell moves Image 5 to the bottom-right.

Design Recommendations

Upload only the images you intend to show together. The grid aims for a balanced near-square layout without manual tuning.
Memory studies: Use fixed, brief durations (e.g., 500 ms) for encoding phases.
Image quality: Use consistent image sizes and aspect ratios for a clean grid appearance.
Grid size: Common layouts are 2x2, 3x3, or 4x4 depending on the number of items.

Common Issues and Solutions

Issue	Solution
Images don't load	Use absolute URLs; check CORS settings; test on the target browser
Grid layout looks uneven	Use images with consistent aspect ratios and dimensions
Too many images for the screen	Reduce image size or grid dimensions; test on target screen resolution

Data Output

Markers and Responses

Markers (stimulus_shown):

{
  "type": "stimulus_shown",
  "ts": "2024-01-01T00:00:01.000Z",
  "hr": 1234.56,
  "data": {
    "type": "images_grid",
    "urls": [
      "https://example.com/img1.jpg",
      "https://example.com/img2.jpg",
      "https://example.com/img3.jpg",
      "https://example.com/img4.jpg"
    ],
    "rows": 2,
    "cols": 2
  }
}

Response Data — recorded once when the participant clicks continue:

{
  "type": "images_grid",
  "viewing_time_ms": 4200,
  "responded": true,
  "resize_metadata": {
    "viewport_width": 1440,
    "viewport_height": 900,
    "device_pixel_ratio": 2,
    "images": [
      { "index": 0, "rendered_width": 462, "rendered_height": 346, "authored_width": 1200, "authored_height": 900, "scale_x": 0.385, "scale_y": 0.3844 },
      { "index": 1, "rendered_width": 462, "rendered_height": 346, "authored_width": 800, "authored_height": 600, "scale_x": 0.5775, "scale_y": 0.5767 }
    ]
  }
}

resize_metadata describes how each image was actually displayed relative to its original size: viewport_width/viewport_height/device_pixel_ratio describe the participant's screen at response time, and each entry in images gives the rendered on-screen size, the image's authored (natural) pixel size, and the scale factor between them for the grid cell at that index (matching the cell's position in the grid, stable even when the grid has empty cells).

Summary Artifact

None. The image grid 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.

Overview​

Where to Configure​

Configuration Parameters​

Grid-Specific Parameters​

Instructions​

Grid Auto-Sizing​

Grid Arrangement​

Participant Flow​

Example​

Design Recommendations​

Common Issues and Solutions​

Data Output​

Markers and Responses​

Summary Artifact​

References​

See Also​