CVI: Response Interval

Written by: Rachel Bennett

At Perkins, we are a gathering place of ideas. The CVI visual behaviors synthesize current research and build on the work of leading theorists in the field. CVI is a lifelong disability and we want to ensure that all individuals with CVI are fully understood. The CVI visual behaviors are an ongoing need, they can change and they can improve for some, but the need never goes away. No one area is separated from the other—the CVI visual behaviors are highly connected and all can impact the individual with CVI at any time.

What is Response Interval?

The length of time from when an item or target is presented and the individual first notices it, looks at it, recognizes it, or responds to it.
The degree of delay in visual attention and delay in visual recognition. Your child might take a long time to look at an object and a long time to understand what they see.
This amount of response time is heavily affected by numerous variables and requires ongoing assessment. Response interval is unique to the individual’s needs.
Response time can change depending on the task, environment, time of day, and how the person with CVI feels.
The length of the delay can correlate with the accessibility of the visual material, clutter or crowding, and noise and motion in the environment. The delay often increases as a result of fatigue or overstimulation.
Increased response time can be one of the initial indicators of visual fatigue.
Inaccessible learning media can lengthen the delay and cause visual fatigue. For example, a student may rapidly respond to tactile or auditory input but have a significant response time when reading a printed passage. This is why a Learning Media Assessment (LMA) is a critical component of the assessment process.
As a person with CVI becomes more familiar and comfortable with the environment, task or items, the response interval may decrease.
Motion and light may elicit quicker visual responses, but these can’t be confused with recognition and understanding of what is seen. Additional time may be required to recognize what is presented.

This CVI behavior is directly impacted by all the other visual behaviors. Clutter, sensory integration, motion, light, color, and visual field abilities can all affect the response time to look at visual stimuli and recognize it. Also, a person with CVI cannot respond to visual stimuli if it can’t be seen or perceived. Response interval may be shorter for some with CVI when items are presented in their stronger visual fields, against a non-cluttered and high contrast background, and they are in a quiet, visually simple, distraction-free environment.

Response interval is a key area that shows how people with CVI have to work much harder when attempting the same visual tasks as their sighted peers.

With an increased visual load, individuals with CVI have to grind it out, as opposed to having that instantaneous capture of information we see with a really efficient visual system.
Dr. Lotfi Merabet, The Science Behind CVI and Visual Fatigue

What are some compensatory strategies related to Response Interval

People with CVI have strategies and workarounds for so much in their daily lives. Compensatory skills help reduce visual search and fatigue and support access to learning. Often other sensory modalities can help be a bridge to perception and understanding, and help decrease the response interval for processing and recognition.

Moving an item or their body to place the item in the accessible visual field
Auditory and/or tactile cues to help establish visual attention and recognition
Rely on additional prompts and language cues from a peer, adult, or teacher
Self-movement to support visual access and/or access to concept development (kinesthetic learning)
Tapping on tables to make items move
Color-coding strategies to support the identification of items
Color to draw one’s visual attention to familiar landmarks
Tactile exploration of items and the environment
Sound cues from objects, people, and the environment
Verbal cues that support the driving of visual attention and recognition
Context to help fill in the gaps in vision and cue past experiences and memory
Predictability and organization to locate items, people, and places in the environment
When visually fatigued, some with CVI may put their heads down, close their eyes, push all items out of view, run away, fall asleep, talk, sing, or tell jokes to change the interaction to an auditory event, yell, or other outward behaviors.

If my son is tired, it will take him more time to look at something and to find something in clutter. He also needs a lot of processing time when it comes to visual recognition. He instantly guesses because he feels like he doesn’t have enough time. But when he has access, which includes using his tactile and auditory skills, and is allowed the time to interpret what he’s looking at, he’ll be able to show you what he knows. He just needs to connect this hard visual task with his prior experiences.
CVI Parent

What are some look fors/questions when observing your child with CVI?

To what extent do certain factors related to presentation and materials affect the speed (increase, decrease, or have no impact) of establishing visual attention and visual recognition? For example, color, clutter, motion, real object vs. two-dimensional image, familiarity with an item?
What is the response interval like when presented with nonvisual stimuli—verbal cues, objects, tactile cues, tactile learning materials, auditory learning materials, or movement-based tasks? Is the response time reduced, increased, or stays the same?
To what extent do these environmental factors affect the speed (increase, decrease, or have no impact) of establishing visual attention and visual recognition? Dim or bright lighting, noise, the motion of people or objects, a cluttered environment, or familiarity with the location?
Does the ability to attend and recognize decrease, increase, or remain the same across the day? Across specific lessons/tasks?
Does the person with CVI consistently avoid or become easily fatigued by certain tasks or activities?
Do they prefer other non-visual sensory channels for specific activities or during certain periods of the day?
Do noisy or busy environments increase signs of fatigue, anxiety, and/or frustration?
Do they show behaviors that may indicate visual fatigue/overload?

I had to reiterate to my child’s school team that she isn’t ‘misbehaving’ when she doesn’t look at the screen or the teacher, or gets up when she needs a break. She’s overwhelmed, she’s visually fatigued, and cannot respond to what’s in front of her.”
CVI Parent

What are some examples of adaptations and accommodations?

All accommodations must be based on individual assessment. The following are meant to inspire and provide a general idea. Accommodations and instructional approaches must be student-specific. Access is individual.

Adapting the environment and learning task is critical to support visual attention and recognition, which will help reduce the amount of effort it takes to use vision. When the environment, learning materials, and tasks are not accessible, then it will require a tremendous amount of energy for the person with CVI to use their vision (and they may not be able to or not want to use vision). Accessibility means that the person with CVI can go through their day and learn without draining all their energy to the point of exhaustion and pain.

With the environmental and task accommodations in place:

Provide the student with opportunities to share what they need to succeed and what works best for them. Self-determination and self-advocacy are essential.
Allow wait time [based on assessment results and task demand] for the person with CVI to establish visual attention, to visually recognize, and to physically respond.
Provide extended time to complete class work, group work, and independent learning tasks.
Allow time to engage in a warm-up activity [individual to each child] to help ease into the learning activity. This activity can be tactile, kinesthetic, auditory, or visual, and must be motivating and easily accessible for the child.
Be methodical and intentional with prompting so as not to overwhelm or disrupt. Directives and prompts are at the right speed (slow and clear) and kept simple and short. The adult stops talking while the student uses their vision or other sensory skills.
Steps and processes in learning activities are clearly conveyed to the student. They have an expectation of the parts of the activity and what the last task of the activity will be. Expectation and prediction will support agency, stamina, and engagement.
Use familiar objects and experiences when introducing new concepts.
Allow the use of other sensory modalities to engage in the learning tasks.

Find more examples from a guide to common CVI IEP accommodations in the CVI Now IEP Guide.

Following the science

Connecting current research of the brain, our visual system, and CVI to better understand the CVI visual behaviors.

“CVI can interfere with any or all aspects of visual processing, from detection to attention, orientation, exploration, search, spatial localization or recognition of objects, scenes, places or faces” (Chokron et al., 2021).
Pilling (2022) surveyed people with CVI about 3-word phrases to indicate a simple strategy to support common visual dysfunctions seen in CVI. For “cannot immediately respond to objects,” “Give me time” was the most popular, and others included “Wait for eight” and “slow the pace.” For other CVI areas: Difficulty maintaining visual attention: “Keep It Short,” Difficulty with busy visual scenes: “Clear the Clutter,” and Variable visual function: “My Vision Varies.”
Increased visual distractors result in increased visual response and search time: “the CVI group showed the largest change in visual search performance as a function of task difficulty. These latter findings are consistent with previous accounts describing impairments with high-order visual processing associated with dorsal stream dysfunction, and in particular, greater impairments in response to increasing task demands and environmental complexity.” (Bennett, et al, 2020)
Serial processing is scrutinizing one piece of information at a time when there is more sensory information to take in, while parallel processing is being able to process many elements of a visual scene at the same time. Serial processing is a less efficient form of visual search. With an increased visual load, individuals with CVI have to grind it out (serial processing), as opposed to having that instantaneous capture of information we see with a really efficient visual system (Dr. Lotfi Merabet from The Science Behind Visual Fatigue).
Responding to visual stimuli requires ocular motor skills to visually attend and sustain eye-to-object contact long enough to facilitate recognition. Fazzi, et al. (2007) notes that “CVI can manifest itself through oculomotor dysfunctions, such as impaired fixation, smooth pursuit, and saccadic movements; strabismus; extrinsic and intrinsic ocular motility abnormalities; and abnormal ocular movements. Fixation and smooth pursuit can be absent (in the subjects with the most severe visual impairment) or discontinuous…”
A recent study (Manley et al., 2023) investigated the ability of individuals with CVI to identify objects in two-dimensional:
- “Individuals with CVI tended to search over a larger area in order to identify the object, which parallels their longer reaction times compared to controls.”
- “When individuals with CVI have difficulty identifying an object, they tend to search the image for longer times and make more fixations on the object’s features.”

References

Bennett CR, Bauer CM, Bailin ES, Merabet LB. (2020). Neuroplasticity in cerebral visual impairment (CVI): Assessing functional vision and the neurophysiological correlates of dorsal stream dysfunction. Neuroscience & Biobehavioral Reviews 108 :171 – 181.

Chang, M. Y. & Borchert, M. S. (2020). Advances in the evaluation and management of cortical/cerebral visual impairment in children. Survey of Ophthalmology 65, 708-724.

Chokron, S., Klara, K., & Gordon D. (2021). Cortical Visual Impairments and Learning Disabilities. Frontiers in Human Neuroscience 15, 573.

Dutton, G. & Lueck, A. (2015). Vision and the Brain: Understanding Cerebral Visual Impairment in Children. New York, New York: American Foundation for the Blind Press.

Fazzi, E., et al. (2007). Spectrum of Visual Disorders in Children With Cerebral Visual Impairment. Journal of Child Neurology, 22(3), 294–301. https://doi.org/10.1177/08830738070220030801

Manley, CE, Walter, K., Micheletti, S., Tietjen, M., Cantillon, E., Fazzi, E., Bex, P., Merabet, L (2023). Object identification in cerebral visual impairment characterized by gaze behavior and image saliency analysis. Brain Dev (2023).

Philip, S.S. and Dutton, G.N. (2014), Cerebral visual impairment in children: a review. Clin Exp Optom, 97: 196-208.

Pilling, R.F. (2022) Make it easier: 3-word strategies to help children with cerebral visual impairment use their vision more effectively. Eye.

Pilling, R.F., Allen, L., Bowman, R. et al. (2022). Clinical assessment, investigation, diagnosis and initial management of cerebral visual impairment: a consensus practice guide. Eye.

Ray, D., et al. (2020). Large-scale Functional Integration, Rather than Functional Dissociation along Dorsal and Ventral Streams, Underlies Visual Perception and Action. J Cogn Neurosci 32 (5): 847–861.

Roman-Lantzy, C. (2018). Cortical Visual Impairment: An Approach to Assessment and Intervention. 2nd ed., New York, NY: AFB Press.

White, A. L., Palmer, J., & Boynton, G. M. (2018). Evidence of Serial Processing in Visual Word Recognition. Psychological science, 29(7), 1062–1071. https://doi.org/10.1177/0956797617751898

Zihl, J., & Dutton, G. N. (2015). Cerebral Visual Impairment in Children: Visuoperceptive and visuocognitieve disorders. Wien: Springer.