6.3 Assessment of Augmentative & Alternative Communication (AAC)
Key Takeaways
- The Participation Model (Beukelman & Mirenda) provides the framework for AAC assessment, requiring systemic identification of opportunity barriers (policy, practice, attitude, knowledge, skill) and access barriers.
- Feature Matching is the core assessment process that systematically aligns an individual's motor, cognitive, linguistic, visual, and auditory capabilities with specific SGD hardware and software features.
- Motor access evaluations compare Direct Selection (finger touch, eye gaze, head tracking) against Indirect Selection (single-switch, step, or automatic scanning) to determine optimal control interfaces and dwell parameters.
- Vocabulary organization must balance Core Vocabulary (high-frequency, multi-context words making up 75–80% of daily communication) with custom Fringe Vocabulary (context-specific nouns).
- Assessment protocols for progressive conditions like Amyotrophic Lateral Sclerosis (ALS) must incorporate proactive timing triggers (e.g., speech rate dropping below 120 wpm) and voice/message banking protocols prior to loss of speech.
6.3 Assessment of Augmentative & Alternative Communication (AAC)
Augmentative and Alternative Communication (AAC) assessment is an ongoing, feature-matching evaluation process designed to supplement or replace restricted natural speech and written communication. Grounded in the Participation Model formulated by Beukelman and Mirenda, AAC assessment does not adhere to prerequisite cognitive or linguistic thresholds. Instead, it systematically identifies participation barriers, evaluates user capabilities across multi-disciplinary domains, and executes feature matching to select appropriate non-electronic (no-tech), low-tech, mid-tech, or high-tech speech-generating devices (SGDs).
The Participation Model & Barrier Analysis
The assessment framework evaluates how the user interacts within their natural communication environments (home, school, workplace, community) relative to same-age peers:
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| PARTICIPATION BARRIER TAXONOMY |
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| Barrier Category | Type | Description & Clinical Example |
+-------------------+---------------------+---------------------------------------------------------+
| Opportunity | Policy Barrier | Legislative/administrative rules restricting device |
| Barriers | | funding or restricting SGD use in school environments. |
| (Imposed by | Practice Barrier | Established routines (e.g., keeping SGD locked away |
| environment/ | | during recess) that restrict communication access. |
| society) | Attitude Barrier | Negative beliefs or low expectations held by family, |
| | | teachers, or staff regarding user potential. |
| | Knowledge Barrier | Lack of awareness regarding AAC options or strategies |
| | | among primary communication partners. |
| | Skill Barrier | Inability of communication partners to program or |
| | | operationalize the device effectively. |
+-------------------+---------------------+---------------------------------------------------------+
| Access Barriers | User Capabilities | Limitations in motor control, sensory-perceptual |
| (Imposed by | & Constraints | processing, cognitive-linguistic skills, or literacy. |
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Comprehensive Capability Assessment Domains
1. Motor Access & Selection Methods
Evaluating physical access to determine how the user will trigger messages:
- Direct Selection: The user selects targets directly using a body part or physical tool.
- Methods: Finger touch, physical stylus, head-pointer, eye-gaze tracking (evaluating pupil calibration, dwell time [e.g., 300–800 ms], blink activation), or head-tracking via optical sensors.
- Assessment Focus: Evaluating range of motion, motor control, muscle endurance, keyguard necessity, and fatigue over time.
- Indirect Selection (Scanning): Used when severe motor impairment precludes direct selection.
- Scanning Patterns: Circular scanning, linear scanning, or grid/column-row scanning.
- Control Techniques: Automatic Scanning (indicator moves continuously; user hits switch to select), Step Scanning (user hits switch 1 repeatedly to advance cursor, hits switch 2 to select), or Inverse Scanning (user holds switch down to advance cursor, releases to select).
- Switch Site Assessment: Evaluating reliable motor sites (hand, head tilt, chin, knee, foot, EMG muscle twitch) for minimal muscle fatigue and fast release time.
2. Sensory & Perceptual Evaluation
- Visual Capabilities: Assessing visual acuity, visual field defects (e.g., visual neglect, hemianopia), cortical visual impairment (CVI), visual contrast sensitivity, and optimal grid size/icon layout (e.g., 4-location vs. 60-location dynamic display).
- Auditory Capabilities: Assessing hearing acuity for auditory scanning cues and synthesized speech output perception.
3. Cognitive-Linguistic & Symbol Assessment
Determining the appropriate representation system and vocabulary structure:
- Symbol Hierarchy Testing: Evaluating comprehension of real objects $\rightarrow$ miniature objects $\rightarrow$ color photographs $\rightarrow$ black-and-white line drawings (e.g., Picture Communication Symbols [PCS], SymbolStix) $\rightarrow$ abstract symbols (Blissymbols) $\rightarrow$ orthographic text.
- Literacy Status: Classifying user literacy to dictate interface design:
- Pre-literate: Symbols organized by functional daily activities.
- Emergent Literate: Combining symbols with initial-letter spelling boards.
- Literate: Text-to-speech SGDs with advanced word prediction engines, abbreviation expansion, and full QWERTY keyboard layouts.
Vocabulary Selection & Organizational Architectures
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| CORE VS. FRINGE VOCABULARY COMPARISON |
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| Parameter | Core Vocabulary | Fringe Vocabulary |
+----------------------+--------------------------------------+-------------------------------------+
| Proportion of Output | 75% – 80% of total daily words spoken| 20% – 25% of total words spoken |
| Word Classes | Verbs, pronouns, adjectives, | Context-specific nouns, specialized |
| | prepositions (e.g., go, stop, I, turn)| terminology (e.g., dinosaur, pizza) |
| Context Flexibility | High; usable across all environments | Low; environment/topic restricted |
| Symbol Representation| Dynamic symbol grids, motor planning | Categorized sub-pages or custom |
| | layouts (e.g., LAMP Words for Life) | visual scene displays (VSDs) |
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Organizational Paradigms
- Pragmatic Organization Dynamic Display (PODD): Vocabulary organized by pragmatic communication intent (e.g., "I want to say something", "Something is wrong") to maintain conversational flow.
- Semantic Compaction (Minspeak / Unity): Uses multi-meaning icon sequences to encode words, reducing the total number of key selections needed for complex text generation.
Proactive Assessment Protocol in Progressive Neurodegenerative Conditions (ALS Focus)
AAC evaluation in progressive conditions like Amyotrophic Lateral Sclerosis (ALS) requires a staged proactive protocol rather than reactive intervention:
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| ALS AAC ASSESSMENT TIMELINE STAGING |
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| Stage | Clinical Indicators & Intervention Action |
+----------------------+------------------------------------------------------------+
| Early Stage | Speech rate >120 wpm; sentence intelligibility 100%. |
| (Preservation) | Action: Educate on AAC options; complete Voice Banking & |
| | Message Banking (e.g., ModelTalker, Tobii Dynavox). |
+----------------------+------------------------------------------------------------+
| Middle Stage | Speech rate drops below 120 wpm; intelligibility decreases.|
| (Feature Matching) | Action: Conduct formal AAC Feature Matching evaluation; |
| | trial high-tech SGD with eye-gaze and head-tracking. |
+----------------------+------------------------------------------------------------+
| Late Stage | Natural speech non-functional; severe quadriparesis. |
| (Implementation) | Action: Deploy eye-gaze high-tech SGD with low-tech |
| | eye-gaze board back-up (e.g., E-Tran frame). |
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A school-based SLP recommends a high-tech speech-generating device (SGD) for an 8-year-old student with non-verbal cerebral palsy. The school district's special education director rejects the purchase, stating that high-tech devices are not permitted for elementary students per district internal policy. According to the Participation Model (Beukelman & Mirenda), which barrier is restricting access?
An SLP is conducting a motor access assessment for a teenager with severe spastic tetraplegia who cannot utilize direct finger selection. The SLP sets up a single-switch system on a dynamic display SGD. The cursor automatically moves across columns and rows, and the user must hit the switch at the precise moment the target highlighted to make a selection. Which access method is being evaluated?
An SLP is establishing a speech preservation plan for a patient recently diagnosed with Amyotrophic Lateral Sclerosis (ALS). The patient currently demonstrates a speaking rate of 145 words per minute (wpm) with 98% sentence intelligibility. According to evidence-based ALS AAC assessment guidelines, what is the most appropriate immediate clinical action?
When designing an AAC symbol display for a non-verbal child with developmental language delays, the SLP dedicates 80% of the display to words such as 'go', 'more', 'want', 'stop', 'help', and 'different'. What type of vocabulary is being prioritized?