Add a stimulus to your interview

A stimulus is something you show a participant mid-interview: an image, a video, a website, an embed, a written concept, or an interactive Figma prototype. Adding one creates a media block: a container holding that one piece of media plus any questions you want asked about it. The media appears on the participant's screen and stays visible for every question inside the block, then comes down when the block ends. Questions inside appear as a card overlaid on the media. If you turn on Split view in project settings, they instead take a column of their own beside the media, so nothing is covered.

The media types

For an interactive Figma design, with optional click tracking and goal detection, use a Figma prototype instead (covered in Figma prototypes below).

Add a media block

1. Add a media step

   In Build, click + Add element and pick Image, Video, Website, Embed, or Text from the Usability group. Each creates a media block.

   

2. Upload or paste the source

   Per type:

   • Image: upload from your computer. There's no link option for images.
   • Video: upload, or paste a YouTube/Vimeo link. Other video hosts aren't supported as links; upload the file instead.
   • Website: paste the URL. The site opens in a new tab during the interview, not inside the call window.
   • Embed: paste a URL or the embed code (the builder pulls the link out of the code for you). Only works for sites that allow themselves to be embedded; if a site refuses to load, use Website instead.
   • Text: type the words participants read. There's nothing to upload or paste a link to; the text you write is the stimulus. Use the formatting buttons above the box for bold, italics, underline, a heading, a bulleted or numbered list, a quote, and links. You can also paste straight from a doc or a slide and the formatting comes with it. A link opens in a new tab, with the interview still running behind it, so use one only for a reference a participant may want; when the page itself is what you are testing, use Website.

   Properties shows a preview, so you can confirm the right media loads.

   

3. Add questions inside the block

   Drop open questions, tasks, statements, or survey questions into the same media block. They get asked while the media is visible. A media block can't contain Sections, Randomization blocks, or other media blocks; for those, use a separate section.

   Every media block needs its media, and image, website, embed, text, and prototype blocks also need at least one question or task inside. Video is the exception: a video can stand alone: participants watch it, say they're done, and the interview moves on, so questions inside a video block are optional.

4. Configure video playback (videos only)

   Two settings affect video playback:

   • The participant's microphone is muted while the video plays, so they finish or pause before responding.
   • Pause video to talk is a project-wide study setting (it applies to every video, not just this block). With it on, the AI stays silent during playback and the participant pauses the video when they want to talk.

When the participant reaches the block, the media loads automatically. The moderator introduces it and asks the participant to confirm they can see it. By default, the moderator can't see the media itself, so it relies on what the participant says. Agent vision (beta) lets it look periodically.

Hold interaction until they answer

For a Figma prototype or an Embed, you can stop participants from touching the media until they've answered the question in front of it. On any question or task inside the block, open Advanced and turn on Block interaction until answered. While the moderator asks that item, Strella dims the media and shows a short banner that tells the participant they can't interact yet, with the question on top. Strella removes the dimming and lets the participant interact again when the moderator moves to the next item.

Use it to capture a genuine first reaction ("what's your first impression of this screen?") before the participant starts clicking around. Don't turn it on for a task that asks the participant to do something in the prototype, since it would leave them looking at a screen they're meant to act on but can't touch.

The setting applies only inside a Figma or Embed block. Moving the item to another block, or changing the block to a Website, Image, or Video, turns it off. Turn it back on if the item returns to a Figma or Embed block.

Send participants to a specific page

For a Figma prototype with no Figma connection, or an Embed, you can send participants to a specific page the moment the interview reaches a question. On any question or task inside the block, open Advanced and enter the page's link in Redirect to URL for this question. When the interview reaches that question, the media reloads at that page. Moving on to a question with nothing set leaves the media where it is, and coming back to the question reloads it again.

Use it to reload the media at a known starting page before a new task, or to open the screen a question is about. It works the same on web and in the mobile app. It is independent of Block interaction until answered: set both on the same question to open a fresh page and keep participants from touching it until they answer.

Inside a Figma prototype, the link must be one Figma can embed, such as a prototype share link. Strella saves it in the form Figma uses for embedding, so the field shows a longer version of the link when you come back to the question.

The setting applies only inside a Figma or Embed block, and inside a Figma block only before you connect it. Once you connect Figma and import the prototype, the block manages its own screens and the setting does not apply. Moving the item out of a Figma or Embed block, or changing the block to a Website, Image, or Video, clears the link, the same way it turns off Block interaction until answered. Changing an Embed block to a Figma prototype keeps the link. If Figma can't embed it, the field shows an error until you replace it.

Watermark sensitive media

A watermark marks unreleased or confidential media with a code unique to each participant, so a screenshot shared outside the study can be attributed to the participant who took it. It discourages sharing and makes a shared screenshot attributable; it doesn't stop a participant from capturing the screen.

To turn it on, select an Image, Video, Embed, or Prototype block, open Advanced, and turn on Watermark. Website and Text blocks don't have the option: a website opens in its own tab, outside the call window.

What participants see

A repeating diagonal mark covers the media. It reads the participant's code, "Strella", and the date the participant joined the study, for example K7QM9WR4 - Strella - 2026-09-28. The mark is semi-transparent and never blocks clicks, scrolling, or playback. The code is an eight-character identifier, not the participant's name or email.

• Images carry the mark inside the image file, so a participant who saves the image gets the watermarked copy.
• Videos, embeds, and prototypes have the mark drawn over them in the call window. Watermarked embeds and prototypes can't be switched to fullscreen. Watermarked videos can't go fullscreen in Chrome or Edge. Firefox and Safari let a participant take a watermarked video fullscreen, and the mark does not cover a fullscreen video.
• In the mobile app, only images carry the watermark.

When someone tries to remove it

If a participant hides or deletes the watermark in their browser, it comes straight back, and a banner warns them that tampering conflicts with the terms and conditions. Strella records the attempt on the interview:

• The participant's quality checks show Fraud detected, with the time of each attempt in the recording, so you can jump to it. A mobile app session records screenshot attempts the same way.
• Strella emails the teammate who created the project after the first attempt in an interview, with a link to that interview.

Strella flags the check for your review. The check alone doesn't change whether Strella recommends accepting the participant.

What it doesn't prevent

• A screenshot, a screen recording, or a phone photo of the screen. The watermark makes the copy traceable. It doesn't block the copy.
• A participant who is determined to strip the mark from a video, embed, or prototype, since it's drawn over those in the browser rather than into the media. Images are the most robust, because the mark is part of the file.

Figma prototypes

A Prototype step embeds a Figma prototype in the call. The participant explores it live, and the moderator asks about their reactions.

There are two modes:

• Default (no Figma connection). Paste the prototype share link. That's it. Participants explore the prototype inside the call window, and the task ends the normal way (the participant says they're done, or uses the end-task control). No screen picker, no goal detection, no click tracking. Pressing Import without a connection is fine: the prototype is embedded and Strella records no clicks. You can still control where a participant lands with Send participants to a specific page.
• Connected to Figma (per researcher). Connect your Figma account from the builder. This imports the prototype's screen list and unlocks goal-based tasks, start-screen pickers, and click tracking.

Use the prototype share link from Figma (a figma.com link to a prototype, design, or file). A website published from Figma Make or Figma Sites is not a prototype. Add it as a Website or Embed instead.

Steps

1. Add a Prototype step

   In Build, click + Add element → Prototype (under the Usability group).

2. Paste the prototype link

   Use the published prototype URL, the one Figma gives you when you share. If the prototype loads in the preview, you're good for default mode.

3. (Optional) Connect Figma to unlock the screen-aware extras

   Click Connect next to the prototype card and authorize Figma. The connection belongs to you inside the organization you are working in. Teammates who author prototype steps each connect their own. Connecting in another organization disconnects this one. See Connect Figma.

   Once connected, choose Import Figma prototype to pull in the prototype's screen list. The prototype's share permission in Figma must be set to Anyone with can view. Otherwise the import can't read it. If you change the design later, use the refresh control to re-import; newly added or renamed screens may require re-picking your selections.

4. Add a Task inside the prototype's block

   Set the exploration mode on a Task. The Task options below appear only with Figma connected:

   • Free explore: participant wanders the prototype. Set a Start screen where they begin. The task ends the normal way (participant says they're done, or via the end-task control depending on your task completion handling).
   • Goal based: set both a Start screen and a Goal screen. When the participant reaches the goal screen, the task ends automatically and the moderator moves on, with no confirmation needed.

   With Goal based mode, the click path the participant takes is recorded and appears as a heatmap after the interview.

5. Set the scale (optional)

   Scale prototype fits the prototype to the call window. It suits desktop designs. Mobile designs usually look better at native scale.

6. Write task instructions

   Tell the moderator what success looks like: "find where you'd update your payment method" or "explore for 2 minutes and tell me what feels off." The moderator uses this both to brief the participant and to know when the task is done.

When the participant reaches this step, the prototype loads in the call window. The moderator introduces the task and watches them work. After the interview, Strella generates a click heatmap (for goal-based tasks on imported prototypes).

Best practices

• Keep questions inside the block, with the visual: questions placed before or after fire when the media isn't on screen, so participants answer about something they can't see. See Best practices.
• Use real URLs only: no example.com or placeholder links; if you don't have the real one yet, leave the media empty and add it later.
• Nest a task under the media, and keep tasks prescriptive and granular: tell the participant exactly what to do.
• In front of a prototype, use a task, not a question: open questions about a static prototype get shallow answers; a task ("find where you'd update billing") forces real interaction. For open exploration, frame that as a task too.

Tips

• Websites open in a new tab: pair website tasks with screen-share recording so the moderator can see what the participant does.
• Keep videos short (under 2 minutes if possible): long videos use up interview time and the participant's attention.
• For mobile-app reactions, you'll need screen-share. The participant shares their phone screen during the interview.
• Goal-based prototype tasks need a real goal screen. "Settings page" is a goal; "the right page" is not.
• Test the prototype yourself with Preview. Broken Figma links don't show up until they break for a participant.
• The participant doesn't see your prototype screen list: they see the prototype as you'd ship it. If you want them to hop between flows, design the prototype that way.
• If a prototype or embed fails to load, the participant can tell the moderator and it'll trigger a reload.

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