Domain: Humanities and Social Sciences — Linguistics
Target concept: An experiment on the spectral characteristics of fricatives and nasals

Video generation prompt: A microphone is connected to a computer, and the speaker uses this microphone to record continuous fricatives (/θ/) and nasals (/n/). The spectrogram on the left shows the fricative in the speech analysis software, while the spectrogram on the right shows the nasal, used for comparing the differences between the two.

Evaluation guide:
(i) Target concept: Spectral distinction between aperiodic fricative turbulence and quasi-periodic nasal resonance.
Minimum mechanism: Speaker must produce linguistically accurate /θ/ and /n/ with correct articulation; microphone must capture acoustic signal; software must compute and render spectrograms in real time with physics-consistent frequency resolution and amplitude scaling.
(ii)Storyline: [Frame 0–10]: Speaker faces camera, microphone centered below mouth; [Frame 11–30]: /θ/ produced → left spectrogram activates with broadband noise; [Frame 31–50]: /n/ produced → right spectrogram activates with formants; [Frame 51–60]: Both spectrograms remain visible side-by-side for direct comparison; perspective is fixed frontal view, full visibility of mouth, mic, and screen; no occlusion, no UI intrusion, no editing cuts.

Manual:
Experimental Procedure
1. Speaker positions lips near microphone; produces sustained /θ/ ("th" in "think") for ~2 seconds.
2. Same speaker immediately produces sustained /n/ ("n" in "noon") for ~2 seconds.
3. Computer screen displays two synchronized spectrograms side-by-side: left for /θ/, right for /n/.
Observation of Experimental Phenomena
Left spectrogram shows broad, featureless high-frequency noise; right spectrogram shows concentrated low-frequency energy with two clear, stable formants and no high-frequency noise.
Summary of Experimental Principles
Fricatives (/θ/) are aperiodic sounds produced by turbulent airflow, yielding broadband noise on spectrograms. Nasals (/n/) are quasi-periodic with vocal fold vibration and nasal cavity resonance, yielding formants and suppressed high-frequency energy.

Prompt Grounding rubric:
level_1: No microphone appears in the shot; no computer screen is shown; no spectrogram display of any kind appears; no speaker is visible; nothing in the frame marks one region as /θ/ or the other as /n/.
level_2: A microphone and a computer screen both appear but are not shown connected to each other; only one spectrogram region is visible instead of two, or the two regions do not appear positioned next to each other; neither region carries any /θ/ or /n/ marking.
level_3: The microphone is visibly connected to the computer; the screen shows two spectrogram regions positioned next to each other; the left region is labeled or otherwise marked as /θ/ (text, arrow, or highlight); the right region is labeled or marked as /n/; the speaker's mouth is visible while producing sound; all of these elements from the prompt are present together.
level_4: Everything described at the 3-point level holds, and in addition the microphone shows visible signs of active use (breath or mouth movement close to the grille); the speaker's mouth visibly forms the /θ/ shape (tongue tip between the teeth) and separately the /n/ shape (lips/tongue closure with the mouth otherwise closed); the /θ/ and /n/ labels are legible and stay attached to the correct region; the two-region layout stays fixed and unbroken throughout.
level_5: Everything described at the 4-point level holds, and in addition both spectrogram regions are shown active while the speaker produces /θ/ then /n/ in one continuous take with no visible gap or cut between the two; the /θ/ and /n/ labels stay in place without flickering or swapping regions; no menu, cursor, or other software element ever blocks either spectrogram or the speaker's face.

Scientific and Causal Correctness rubric:
level_1: Both spectrogram regions look the same as each other; or both show the kind of clear striped, vowel-like banded pattern; or both regions stay blank; or the pattern is swapped so the /n/-side region looks like the fricative pattern and the /θ/-side region looks like the nasal pattern.
level_2: One region shows a hazy, all-over noise texture and the other shows a banded pattern, but the assignment is backwards or inconsistent with what the speaker is producing — for example the speaker is making /θ/ while the right (/n/) region is the one that lights up, or the speaker is making /n/ while the left (/θ/) region shows the noisy pattern.
level_3: While the speaker produces /θ/, the left region fills with a hazy, all-over noise texture with no visible banding; while the speaker produces /n/, the right region instead shows two or three low, closely-spaced horizontal bands below roughly 3 kHz, with a visibly emptier region above that; the speaker's mouth shape matches each sound as it is produced (tongue between the teeth for /θ/, closed-mouth nasal posture for /n/); the displayed pattern change tracks what the speaker is doing.
level_4: Everything described at the 3-point level holds, and in addition the /n/ region shows no extra noisy texture bleeding into its upper portion above roughly 2.5 kHz, and the /θ/ region shows no banded, vowel-like structure mixed into its noise; the speaker's mouth posture stays steady for the full duration of each sound rather than shifting partway through.
level_5: Everything described at the 4-point level holds, and in addition the /θ/ region's noise texture fills nearly its whole height, spanning roughly 2–8 kHz, with even, unbroken intensity from one edge of that segment to the other; the /n/ region's low horizontal bands stay steady around roughly 250 Hz and 2000 Hz in position and brightness for the whole /n/ segment, with a clearly empty band above roughly 3 kHz; neither region shows a fade-in/fade-out blur or blending between the two patterns at the boundary between sounds.

Spatiotemporal Consistency rubric:
level_1: A spectrogram region appears or disappears abruptly rather than filling in gradually; the microphone jumps to a different position between frames; the speaker turns more than about 45° to show mostly the side or back of their head, or disappears from frame entirely, partway through the clip; the screen's picture flickers or its resolution visibly changes mid-video; there is an obvious jump-cut, freeze, or repeated frame.
level_2: The microphone visibly shifts sideways or twists more than about 15° relative to the speaker between frames; the two spectrogram regions change size or shape relative to each other; the speaker's mouth moves out of frame while still producing sound; the screen's overall brightness jumps by more than about 30% partway through the clip rather than staying steady; or the lighting/shadow direction visibly changes between the /θ/ and /n/ segments.
level_3: The microphone, screen, and speaker all stay continuously visible and in the same relative position to each other; the microphone keeps the same orientation and distance from the speaker throughout; the speaker's head and mouth stay fully in frame the whole time; the screen never pans, zooms, or rotates; the two spectrogram regions keep the same size, shape, and side-by-side arrangement throughout.
level_4: Everything described at the 3-point level holds, and in addition the borders of the two spectrogram regions stay steady rather than wobbling or drifting frame to frame; the speaker's face shows no sudden unrelated reaction, such as a blink or grimace, that coincides with the switch from /θ/ to /n/; the screen's bezel and the spectrogram's axis lines stay straight and unbroken rather than tearing or glitching.
level_5: Everything described at the 4-point level holds, and in addition the left region visibly fills in only while /θ/ is being produced and stops updating once /θ/ ends, and the right region visibly fills in only while /n/ is being produced and stops once /n/ ends, with no region continuing to update after its sound has stopped or starting before its sound begins; the speaker's tongue and lips move smoothly from the /θ/ articulation to the /n/ articulation without a jump cut or frozen frame in between.